Management of Hazards Associated with Location of Process Plant
TentsAPI RECOMMENDED PRACTICE 756FIRSTEDITION, DRAFT 11 COMMITTEE
DRAFTIIAPI RECOMMENDED PRACTICE 756 FOREWORD API RP 752 (Permanent
Buildings) and API RP 753 (Portable Buildings) do not provide
guidance regardingsiting
evaluationfortents.Thisrecommendedpractice(RP756)providesguidancefortentsitingevaluation.It
references documents concerning technical aspects of siting
evaluation including hazard identification, consequence modeling,
structural analysis, and risk. Among the hazards that potentially
could affect tent occupants are explosion, fire, and toxic material
releases. Nothing contained in any API publication is to be
construed as granting any right, by implication or otherwise, for
the manufacture, sale, or use of any method, apparatus, or product
covered by letters patent. Neither should anything contained in the
publication be construed as ensuring anyone against liability for
infringement of letters patent. Shall:As used in an RP, shall
denotes a minimum requirement in order to conform to the RP.
Should:As used in an RP, should denotes a recommendation or that
which is advised but not required in order to conform to the
RP.This RP was produced under API standardization procedures that
ensure appropriate notification and participation in
thedevelopmentalprocessandisdesignatedasanAPIstandard.Questionsconcerningtheinterpretationofthe
content of this publication or comments and questions concerning
the procedures under which this publication was developed
shouldbedirectedinwriting to theDirector of Standards,American
PetroleumInstitute, 1220 LStreet,
NW,Washington,DC20005.Requestsforpermissiontoreproduceortranslatealloranypartofthematerial
published herein should also be addressed to the director.
Generally,APIRPsarereviewedandrevised,reaffirmed,orwithdrawnatleasteveryfiveyears.Aone-time
extension of up to twoyears may be added to this review cycle.
Status of the publication can be ascertained from the API Standards
Department, telephone (202) 682-8000. A catalog of API publications
and materials is published annually by API, 1220 L Street, NW,
Washington, DC 20005.
SuggestedrevisionsareinvitedandshouldbesubmittedtotheStandardsDepartment,API,1220LStreet,NW,
Washington, DC 20005, [email protected]. COMMITTEE DRAFTMANAGEMENT
OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTSIII Table
of Contents 1Scope
......................................................................................................................................
1 1.1General
..............................................................................................................................................................
1 1.2Guiding Principles
.............................................................................................................................................
1 1.3Relationship with API RP-752
...........................................................................................................................
1 2Normative References
...........................................................................................................
2 3Terms and Definitions
...........................................................................................................
2 3.1Blast Load
..........................................................................................................................................................
2 3.2Consequence
....................................................................................................................................................
2 3.3Consequence-Based
Approach........................................................................................................................
2 3.4Essential Personnel
..........................................................................................................................................
2 3.5Fabric
.................................................................................................................................................................
2 3.6Hazard
...............................................................................................................................................................
3 3.7Maximum Credible Event(MCE)
.....................................................................................................................
3 3.8Occupant Vulnerability
......................................................................................................................................
3 3.9On-Site Personnel
.............................................................................................................................................
3 3.10Process Area
.....................................................................................................................................................
3 3.11Quantitative Risk Assessment
..........................................................................................................................
3 3.12Risk
....................................................................................................................................................................
3 3.13Risk-Based Approach
.......................................................................................................................................
3 3.14Spacing Tables Approach
.................................................................................................................................
3 3.15Tent
....................................................................................................................................................................
4 3.16Tent Siting Evaluation
.......................................................................................................................................
6 3.17Toxic Material
....................................................................................................................................................
6 3.18Vapor Cloud Explosion (VCE)
..........................................................................................................................
6 4Determination of Tents Requiring Tent Siting Evaluation
................................................ 7 4.1Tents
Included in the Siting Evaluation
............................................................................................................
7 4.2Tents Excluded from the Siting Evaluation
......................................................................................................
7 4.3Tents Evaluated on a Case-by-case Basis
......................................................................................................
8 5Tent Siting Evaluation Processes
........................................................................................
8 5.1Work Process Overview
....................................................................................................................................
8 5.2General Tent Siting Evaluation Processes
.....................................................................................................
10 5.2.1Tent Siting Evaluation Criteria
................................................................................................................
10 5.2.2Siting Evaluation of Tents
.......................................................................................................................
10 5.2.3Selection of Assessment Approach
.......................................................................................................
10 5.2.4Scenario Selection for Consequence-based and Risk-based
Approaches .......................................... 10
5.3Alternative Siting Evaluation Process for Turnaround/Project
Construction Tents ...................................... 11
5.3.1Use of Alternative Approach
...................................................................................................................
11 5.3.2Limitations of Alternative Approach
........................................................................................................
11 5.3.3Alternative Siting Criteria
........................................................................................................................
11 5.3.4Additional Requirements for Turnaround/Project Construction
Tents .................................................. 12
5.4Minimum Tent Standoff
Distances..................................................................................................................
12 5.5Additional Design and Siting Requirements for Tents Included
in the Siting Evaluation Study ................... 13
5.6Considerations for Tents Excluded from the Siting Evaluation
Study ...........................................................
13 5.7Personnel Performing Tent Siting Evaluation
................................................................................................
14 5.8Management of Tent Occupancy
...................................................................................................................
14 5.9Implementation and Change Control
..............................................................................................................
14 5.10Documentation
................................................................................................................................................
15 6Tent Siting Evaluation for Explosion
.................................................................................
15 6.1Siting and Design of Tents for
Explosions......................................................................................................
15 6.2Work Process Overview
..................................................................................................................................
15 COMMITTEE DRAFTIVAPI RECOMMENDED PRACTICE 756 6.3Tent Siting
Methodology
.................................................................................................................................
17 6.4Detailed Structural Analysis
............................................................................................................................
18 6.5Explosion Testing
............................................................................................................................................
18 6.6Measures to Reduce Occupant Vulnerability from Explosions
.....................................................................
18 7Tent Siting Evaluation for Fire
...........................................................................................
19 7.1Siting and Design of Tents for Fire
.................................................................................................................
19 7.2Work Process
..................................................................................................................................................
19 7.3Spacing Table Approach
.................................................................................................................................
21 7.4Detailed Analysis
.............................................................................................................................................
21 7.4.1Determining the Fire Effects at Tent Location
.......................................................................................
21 7.4.2Occupant Vulnerability from Fire
............................................................................................................
21 7.5Egress and Evacuation for Fire
......................................................................................................................
21 7.5.1Emergency Response Features
.............................................................................................................
21 8Tent Siting Evaluation for Toxic Material Release
........................................................... 22
8.1Siting and Design of Tents for Toxic Material Release
..................................................................................
22 8.2Work Process
..................................................................................................................................................
22 8.3Determining Toxic Impacts on Tent Occupants
.............................................................................................
23 8.4Egress and Evacuation for Toxic Material Release
.......................................................................................
24 List of Tables Table 1.Minimum Tent Standoff Distances
...................................................................................................................
12 List of Figures Figure 1.Example of Air Inflated Structure (Left
Exterior View, Right Typical pressurized tube layout)
................. 4 Figure 2.Examples of Scaffold Structures
.......................................................................................................................
4 Figure 3.Examples of Pole Tents
....................................................................................................................................
5 Figure 4.Example of Light Frame Tent
...........................................................................................................................
5 Figure 5.Examples of Tension Membrane Structures
....................................................................................................
6 Figure 6.Work Process: Tent Siting Evaluation
..............................................................................................................
9 Figure 7.Work Process: Tent Siting Evaluation for Explosion
......................................................................................
16 Figure 8.Tent Siting/Design Guidancefor Explosion Hazards
....................................................................................
17 Figure 9.Work Process: Tent Siting Evaluation for Fire
...............................................................................................
20 Figure 10.Work Process: Tent Siting Evaluation for Toxic Release
............................................................................
23 COMMITTEE DRAFT Management of Hazards Associated with Location
of Process Plant Tents 1Scope 1.1General This recommended practice
(RP) provides guidance for managing the risk from explosions, fires
and toxic material releases to on-site personnel located in
tents.The term tent is used to describe a wide range of structures
and is defined in 3.15.This RP was developed for use at refineries,
petrochemical and chemical operations, natural gas
liquidsextractionplants,naturalgasliquefactionplants,andotheronshorefacilitiescoveredbyOSHA29CFR
1910.119 [Reference 1]. The focus of this RP is primarily on
assessing the impact to tent occupants from process related
hazards. However, non-process related tent hazards may existwhich
could present risks to tent occupants.Previousaccidents have
demonstrated that tent occupants are susceptible to injuries
fromfires originating inside the tent, from tent collapse due to
extreme weather, and from falling objects,Some of these hazards are
managed by tentdesign standards, manufacturers recommendations, and
local regulations. See 5.5 for additional guidance. 1.2Guiding
Principles This RP is based on the following guiding principles:
a)Locate personnel away from process areas consistent with safe and
effective operations. b)Minimize the use of tents intended for
occupancy in close proximity to process areas. c)Manage the
occupancy of tents in close proximity to process areas. d)Design,
construct, install, modify, and maintain tents intended for
occupancy to mitigate hazards that the tent could present to
occupants in the event of explosion, fire, and toxic material
release. e)Manage the use of tents intended for occupancy as an
integral part of the design, construction, maintenance, and
operation of a facility. 1.3Relationship with API RP-752
TherequirementsandworkprocessesinAPIRP-756aresimilartoAPIRP-752,ManagementofHazards
AssociatedwiththeLocationofProcessPlantPermanentBuildings.ImplementationofAPIRP-756couldbe
viewed as an extension of API RP-752, but with application to tents
only.API RP-756 was intentionally written using the same language
in API RP-752 for consistency between the two documents. COMMITTEE
DRAFT2API RECOMMENDED PRACTICE 756 2Normative References The
following are normative references for this RP:
ManagementofHazardsAssociatedwithLocationofProcessPlantPermanentBuildings,API
Recommended Practice 752
ManagementofHazardsAssociatedwithLocationofProcessPlantPortableBuildings,API
Recommended Practice 753 Temporary Structures Tents Safety, EN
13782 References in this document and the bibliography are provided
for information only and are not part of this RP. 3Terms and
DefinitionsFor the purpose of this publication, the following terms
and definitions apply. 3.1Blast Load The load applied to a
structure or object from a blast wave, which is described by the
combination of overpressure and either impulse or duration.
3.2Consequence The potential effects of an explosion, fire, or
toxic material release.Consequence descriptions may be qualitative
or quantitative.3.3Consequence-Based Approach The methodology used
for tent siting evaluation that is based on the impact of
explosion, fire, and/or toxic material release and which does not
consider the frequency of these events 3.4Essential PersonnelOnsite
personnel with specific work activities that require them to be
located intents in or near a process area for logistical and
response purposes. The identification of essential personnel will
vary with operation and work activities
includingnormaloperation,start-up,andplannedshutdown.Examplesofessentialpersonnelinclude,butarenot
limitedto,craftspeople,operators,andmaintenancepersonnel.Examplesofpersonswhoarenotessential
personnelinclude,butarenotlimitedto,designers,timekeepers,clericalstaff,administrativesupport,and
procurement staff.3.5FabricAny flexible material used for the
covering or enclosure of the tent.COMMITTEE DRAFTMANAGEMENT OF
HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS3 3.6Hazard
Aninherentphysicalorchemicalcharacteristic(e.g.flammability,toxicity,corrosivity,storedchemicalenergy,or
mechanical energy) that has the potential for causing harm to
people, property, or the environment. 3.7Maximum Credible
Event(MCE)Ahypotheticalexplosion,fire,ortoxicmaterialreleaseeventthathasthepotentialmaximumconsequencetothe
occupantsofthetentunderconsiderationfromamongthemajorscenariosevaluated.Themajorscenariosare
realisticandhaveareasonableprobabilityofoccurrenceconsideringthechemicals,inventories,equipmentand
piping design, operating conditions, fuel reactivity, process unit
geometry, industry incident history, and other factors. Each tent
may have its own set of MCEs for potential explosion, fire, or
toxic material release impacts. 3.8Occupant Vulnerability
Proportionofoccupantsthatcouldpotentiallysufferalifethreateninginjuryorfatalityifapotentialeventwereto
occur.3.9On-Site Personnel Employees, contractors, visitors,
service providers, and others present at the facility.3.10Process
Area An area containing equipment (e.g. pipes, pumps, valves,
vessels, reactors, and supporting structures) intended to process
or store materials with the potential for explosion, fire, or toxic
material release.3.11Quantitative Risk Assessment
Thesystematicdevelopmentofnumericalestimatesoftheexpectedfrequencyandconsequenceofpotential
accidentsbasedonengineeringevaluationandmathematicaltechniques.Thenumericalestimatescanvaryfrom
simple values of probability/frequency of an event occurring based
on relevant historical industry or other available data to very
detailed frequency modeling techniques. 3.12Risk A measure of
potential injury, environmental damage, or economic loss in terms
of both the incident likelihood and the severity of the loss or
injury. 3.13Risk-Based Approach
Aquantitativeriskassessmentmethodologyusedfortentsitingevaluationthattakesintoconsiderationnumerical
values for both the consequences and frequencies of explosion,
fire, or toxic material release. 3.14Spacing Tables Approach
Thespacingtablesapproachusesestablishedtablestodetermineminimumseparationdistancesbetween
equipment and tents.Industry groups, insurance associations,
regulators, and owner/operator companies may have experience-based
spacing tables that are useful for establishing minimum tent
spacing for fire.COMMITTEE DRAFT4API RECOMMENDED PRACTICE 756
3.15TentThetermtentisusedtodescribeawiderangeofstructures.Thesestructuresincludetraditionaltentswithor
withoutsides(canopy),airinflatedstructures,airsupportedstructures,tensionedmembranestructures,scaffold
structures,orstructuresthatuseacombinationoffabricandrigidpanels.Someofthesetenttypesaredefined
below:
Traditionaltent:afabriccoveredstructure,enclosureorshelterthatachievesitssupportbymechanical
means such as columns, beams, poles or arches, rope or cables, or
some combination of these.Air inflated structure:a structure in
which the shape is maintained by air pressurization of cells or
tubes to form a barrel vault over the usable area.The pressurized
areas used to support he structure are not occupied. See Figure 1
below for an example. Figure 1.Example of Air Inflated Structure
(Left Exterior View, Right Typical pressurized tube layout)
Air-supported structures: a structure in whichthe shape is attained
by air pressure, and occupants of this structure are within the
pressurized area. Scaffold structures: a self-supported structure
built with scaffolding components and enclosed with a fabric,
membrane or other similar material.See Figure 2 below for examples
of scaffold structures.
Figure 2.Examples of Scaffold StructuresCOMMITTEE
DRAFTMANAGEMENT OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS
PLANT TENTS5 Pole tent: a fabric covered structure that achieves
its support by use of columns/poles and is stabilized along
theperimeterwithropes/cables.Poletentsareavailableinwind-ratedandnon-wind-rateddesigns.See
Figure 3 for examples of pole tents. Figure 3.Examples of Pole
Tents
Lightframetent:afabriccoveredstructurethatusesametalframetomaintainitsshapeandisstabilized
along the perimeter with ropes/cables. Unlike pole tents, the light
frame tents have no center poles.Structural
membersarelocatedaroundtheperimeterandtheuprightmembersarerigidlysecuredtotheroofframe
members.Lightframetentsareavailableinwind-ratedandnon-wind-rateddesigns.SeeFigure4foran
example of a light frame tent.. Figure 4.Example of Light Frame
Tent COMMITTEE DRAFT6API RECOMMENDED PRACTICE 756
Tensionedmembranestructures:astructureincorporatingamembraneandastructuralsupportsystem
such as arches, columns, and cables or beams.The stresses developed
in the tensioned membrane interact with those in the structural
support so that the entire assembly acts together to resist the
applied load.Tension membrane tents differ from light frame tents
in that:Tension membrane tents have a much more robust frame,The
frame is directly anchored to the ground (no staked ropes/cables
along the perimeter), and The fabric is taut. Most, if not all,
tension membrane structures are wind-rated. See Figure 5 below for
examples of tension Membrane tents. Figure 5.Examples of Tension
Membrane Structures 3.16Tent Siting EvaluationThe procedures
described in this RP that are used to evaluate the hazards and
establish the design criteria for tents at their specific location.
3.17Toxic Material An airborne agent that could result in acute
adverse human health effects. 3.18Vapor Cloud Explosion (VCE)
Theexplosionresultingfromtheignitionofacloudofflammablevapor,gas,ormistinwhichtheflamespeed
accelerates to sufficiently high velocities to produce a damaging
blast wave. COMMITTEE DRAFTMANAGEMENT OF HAZARDS ASSOCIATED WITH
LOCATION OF PROCESS PLANT TENTS7 4Determination of Tents Requiring
Tent Siting Evaluation 4.1Tents Included in the Siting Evaluation
Tents intended for occupancy shall be included in the tent siting
evaluation study. A tent intended for occupancy has personnel
assigned to it, or is used for a recurring personnel
function.Examples of such tents include, but are not limited to
tents being used for: Breaks or meals. Weather shelters (e.g., cool
down and warm-up tents). Change houses, orientation, training, or
meetings. With assignedpersonnel such
asguardhouses,toolstations,maintenance shops, field operator
shelters, offices, laboratories, or warehouses. Tents for
fabrication or equipment assembly that can be performed remotely
from the process unit. Certain tents may be excluded from the
evaluation as described in4.2. Buildings that are locatedinside of
tents are covered by either API RP-752 or API RP-753. 4.2Tents
Excluded from the Siting EvaluationExamples of tents that may be
excluded from the tent siting evaluation are as follows.
a)Temporarytentsthatprovideweatherprotectionastheirprimaryfunctionforequipmentorworkactivitiesthat
cannotbefeasiblyperformedremotelyfromtheprocessunit.Examplesofsuchworkactivitiesinthese
temporary tents include, but are not limited to: WeldingNon
Destructive Testing (NDT)Hazardous materials abatement or
decontaminationCatalyst loading and unloading Covering open
equipmentRepair of equipment (e.g., compressors / turbines)
b)Tentsthatencloseprocessareaswhereonlyessentialpersonnelareassignedtoperformactivitiessimilarto
thoseperformedatanoutdoorprocessarea.Thebasisforexcludingsuchtentsistherecognitionthatcertain
work activities must be performed in or near the process area(e.g.,
a tent enclosing an operating compressor). c)Individual small,
lightweight tents (i.e., less than about 150 sq ft). The basis for
excluding such tents is that the number of occupants is low, and
the risks inside and outside the tent are not significantly
different.Installation of multiple small contiguous tents to
perform the function of a larger tent is not covered by this
exclusion. d)Tents that require, at most, intermittent access.The
basis for excluding such tents is that a person would only spend a
very small amount of time inside the tent and only a small number
of people would be present at any one time. Examples of such tents
include, but are not limited to: Tents intended to protect
equipment or product (with no personnel assigned). Field
sampling/testing stations. COMMITTEE DRAFT8API RECOMMENDED PRACTICE
756 Analyzer stations. Hydration stations (a shaded area that
provides access to liquids with no other amenities). Safety shower
tents.
e)Temporarycool-downorwarm-uptentsintendedtomeetowner/operatorindustrialhygienerequirementsfor
extreme environmental conditions (e.g.,wherepeoplecanwork in the
environment for 5 minutes, butneed20
minutesinsidethetentforthermalrecovery).Thebasisforexcludingsuchtentsisthatthereislimited
occupancy by essential personnel, the fact that locating the tent
further away would increase extreme heat/cold exposure for
personnel, and where the use of alternatives (such as Blast
Resistant Modules) is not practicable.
Tentsthatareexcludedfromthetentsitingevaluationshallnotbeusedbypersonnelforotherthantheoriginal
intended use (e.g., a welding shelter shall not be used as a break
area).4.3Tents Evaluated on a Case-by-case BasisTents that do not
meet the descriptions provided in 4.1 or 4.2 above may be included
or excluded in the tent siting evaluation on a case-by-case
basis.The basis for the tents inclusion or exclusion should
consider the hazards, the number of tent occupants, how much time
(frequency and duration) occupants are in the tent, and the purpose
of the tent. 5Tent Siting Evaluation Processes 5.1Work Process
Overview The work process for tent siting evaluations can be
summarized in three steps: 1.Identify tents that are to be included
in the siting evaluation study. 2.Evaluate these tents against
potential explosion, fire, and toxic impacts.
3.Determineiftentdesign/sitingmeetstheowner/operatorstentsitingevaluationcriteria.Mitigatethe
consequences or risk where required by applying the additional
design/siting requirements (see 5.5). Tents excluded from the
siting evaluation study may consider the siting/layout suggestions
in 5.6. See Figure 6 for an overview of the tent siting evaluation
work process. COMMITTEE DRAFTMANAGEMENT OF HAZARDS ASSOCIATED WITH
LOCATION OF PROCESS PLANT TENTS9 Figure 6.Work Process: Tent Siting
Evaluation COMMITTEE DRAFT10API RECOMMENDED PRACTICE 756 5.2General
Tent Siting Evaluation Processes 5.2.1Tent Siting Evaluation
CriteriaPrior to starting a tent siting evaluation,
owners/operators should select the tent siting evaluation criteria
consistent
withtheselectedassessmentapproach(es)describedin5.2.3below.RefertoAPIRP-752Section5.3fora
description of the evaluation criteria for each of the assessment
approaches. 5.2.2Siting Evaluation of TentsOwners/operators shall
carry out siting evaluations for tents included in the tent siting
evaluation study in accordance
withSection6,7,and8ofthisRP,orforalternativelyinaccordancewith5.3for
turnaround/project construction tents. Additional tent
design/siting requirements are provided in 5.5 and 5.6.
5.2.3Selection of Assessment Approach
Owners/operatorsmaychooseoneormoreofthefollowingapproachesforassessingexplosion,fireandtoxic
material release scenarios.a) The consequence-based approach
evaluates the impact of explosion, fire, and toxic scenarios. This
approach shall be based on maximum credible events (MCEs) for each
tent and type of hazard
considered.b)Therisk-basedapproachisquantitativeandutilizesnumericalvaluesforboththeconsequencesandthe
frequencies of explosion, fire, and toxic material release
scenarios.
c)Thespacingtablesapproach,utilizedforfirehazardsonly,usesestablishedtablestodetermineminimum
separationdistancesbetweenequipmentandtents.Forexample,DOEstandard1088-95[Reference10]
providesseparationdistanceguidelinesfortents.Thespacingtablesapproachalsoincludesindexmethods
(e.g. Dows Fire & Explosion Index [Reference 2] and the Mond
Index [Reference 3]).Industry groups, insurance associations,
regulators, and owner/operator companies may have developed
experience-based spacing tables for minimum tent spacing for
fire.However, these fire-specific tables shall not be used for tent
siting evaluation
forexplosionandtoxicmaterialrelease.Scenarioselectionisnotrequiredforexperience-basedfirespacing
tables.Owners/operators may choose to develop site-specific spacing
distances for each type oftent considered to cover explosions,
fires, or toxic material release. These distances shall be based on
MCEs. The use of site specific, MCE based spacing distances is
considered an application of a consequence-based approach and not
the spacing tables approach as discussed above.
Theconsequence-basedandrisk-basedapproachesmayrangefromsimpletocomplexanalyses.Complex
analysescantakeintoaccountdetailsofthesitelayout,geometry,andthescenarios.Simplifiedanalysesshould
useconservativeassumptionsasameanstoaccountforthedetailsnotincludedintheanalyses.Additional
guidance may be found in Sections 6, 7, and 8 of this RP.
5.2.4Scenario Selection for Consequence-based and Risk-based
Approaches The scenario selection process includes, where
applicable, hazards associated with the operations including loss
of containment, releases from flares, process vent stacks, and
atmospheric relief devices.The scenarios should be based primarily
on the process area-specific factors such as equipment failure rate
data, design of the equipment in the process area, process stream
composition, and operating conditions. Consideration
shouldbegiventorelevantcompanyandindustrylossofcontainmentdataforsimilartypesofprocessesand
equipment when selecting scenarios.Start-up, shutdown and emergency
shutdown situations should be included in the scenario selection
process.A review of the process hazard analysis (PHA) may assist in
identifying scenarios. COMMITTEE DRAFTMANAGEMENT OF HAZARDS
ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS11 5.3Alternative
Siting Evaluation Process for Turnaround/Project Construction Tents
5.3.1Use of Alternative Approach
AnalternativeapproachmaybeusedforthesitingofTurnaround/ProjectConstructiontentsthatmeetthe
limitations specified in 5.3.2. The alternative approach uses a
default siting distance of 330 ft from the nearest edge
ofactiveprocessareaswithVCE,fire,ortoxichazard(s).Inmostcases,thealternativeapproachrequiresless
analysis than the evaluation processes described in Sections 6, 7,
and 8 of this RP. The alternative approach is based on the
following.There is aneed to locatelargenumbers of peopletosupport
these activities and the risks of transporting people may be
significant. Risks are lower with unit shutdown. Tents, due to
their liqht-weight nature, provide low vulnerability.Tents can be
rapidly evacuated (5.3.4). Tents have additional risk mitigation
(5.3.4). It is not practical to use blast resistant modules due to
the need to house large occupancies
Thealternativeapproachcoversexplosions,fire,andtoxics.Theowner/operatorshoulddocumentwhetherthis
approachissuitablefortheirspecificapplicationbyconsideringthepeakoccupancy,thetotalcumulative
occupancy,thedurationthetentwillbeinuse,andanyunusualrisksthatmayexist,suchasfromadjacent
operating units near the tent location, inventory on the unit that
is shutdown, consideration of drifting clouds into the unit that is
shutdown, etc.5.3.2Limitations of Alternative Approach The
alternative approach shall be used only for specific turnaround
tents/project construction tents that meet all the following
conditions:
Thetentsareoccupiedonlybyessentialpersonnelwhoareassignedtoworkinthespecific
process/construction areas.Personnel not assigned to the specific
turnaround or the units construction are not permitted to occupy
the tent.
Individualsareallowedinthetentonlyforshortdurations(e.g.,breaks,meals,orworkrelatedsafety
meetings). The tent is occupied only for the duration of the
turnaround or project construction. The tent may not be used for
other purposes (e.g., celebrations, award meetings). The tent shall
not have walls or roofs that are rigid (e.g., plywood, sheet metal)
unless the tent is designed for the blast loads. The tent shall not
be constructed from scaffolding. 5.3.3Alternative Siting Criteria
Whenusingthealternativesitingevaluationprocess,turnaround/projectconstructiontentsmaybelocated330
ft from the nearest edge of active process areas with VCE, fire, or
toxic hazard(s). COMMITTEE DRAFT12API RECOMMENDED PRACTICE 756
Useof a smaller standoff distance is
permittedwithadditionaldetailedanalysisprovided that the results
meet the owner/operator criteria.The analysis may be consequence or
risk based.This additional assessment may consider the following:
Risksofthepersonnelinthetentforashortdurationrelativetotheriskofthepersonnellocatedattheir
assigned work area. Risks of transporting personnel between the
tent and the assigned work area. Traffic risks to personnel.Process
hazard risks exposures along the personnel travel routes.
Construction risks along the personnel travel route. Site security
issues. 5.3.4Additional Requirements for Turnaround/Project
Construction TentsTents should not be occupied during times of high
risk (e.g., adjacent unit start-up and planned unit shutdowns).
Owners/operatorsshouldimplementthemeasuresdescribedin6.6fortentsexposedtoexplosionhazards,and
shall have tent evacuation plans in accordance with 7 (fire) and 8
(toxic), as applicable.
Theselectedtentlocationshallmeetowner/operatorspecifiedseparationdistancesfromspecificequipment
(electrical area classification, distances from tanks, flares,
sewers, etc.).See5.5 and 5.6 for details.The tent siting shall be
reevaluated when risks might increase, such as in the following
situations: When a significant amount of congestion has been
created (e.g., by the project) producing the potential for a VCE,
When hydrocarbon is introduced into the unit, orWhen there is
adjacent crane erection activity. 5.4Minimum Tent Standoff
Distances The minimum standoff distances for tents that are
included in the tent siting evaluation are summarized inTable 1
below.Thegeneralworkprocess(describedin5.2)maybeusedforanytent.Thealternativetentsiting
evaluation process is applicable ONLY for turnaround tents/project
construction tents as defined in 5.3.2. Table 1.Minimum Tent
Standoff Distances Tent UseWork Process Minimum Standoff Distance
Explosion Hazard Fire HazardToxic Hazard AnyGeneral (See 5.2) See
Section 6See Section 7See Section 8 Turnaround orProject
Construction Alternative (See 5.3) 330 ft unless a detailed
analysis is performed COMMITTEE DRAFTMANAGEMENT OF HAZARDS
ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS13
5.5AdditionalDesignandSitingRequirementsforTentsIncludedintheSiting
Evaluation Study Owners/operators should verify that all tents
included in the siting evaluation study:
Complywithanyactivitylimitations,occupancyloading,design,orspacingandsitingrequirementsfrom
local and national/jurisdictional fire codes. Have adequate tent
egress/exits. This may be covered by the local fire codes (e.g.,
NFPA 101Life Safety Code [Reference 8] and NFPA 102 Standard for
Grandstands, Folding and Telescoping Seating, Tents and Membrane
Structures [Reference 9]) or company policy.Are not placed within
the dike, berm or bund areas of storage tanks containing flammable,
combustible or toxic material. Use fire resistant fabrics
consistent with local standards as required. Are sited consistent
with the sites safe working practices.
Owners/operatorsshouldconsiderpotentialhazardswhensitingtents.Theseinclude,butarenotlimitedto,the
following: Proximity to flares, vent stacks, and atmospheric relief
valves. Proximity to sewers and vents.Proximity to cranes, heavy
lift activities, and vehicle traffic.
Obstructionstoescaperoutesbytentcomponents(e.g.,guywiresshouldbemarked/flaggedtomitigate
potential tripping hazard). It should be recognized that some tents
are not designed for significant weather events (lightning, high
winds, snow
storms,etc.)andalltentshavelimitstotheirstructuralcapacity.Owners/operatorsshouldconsiderlocal
environmentalconditionsandlocalbuildingcodeswhenselecting,constructing,andmaintainingtents.Owners/operators
should have a procedure in place to evacuate a tent in the event
that environmental loading could exceed the tents structural
capacity. 5.6Considerations for Tents Excluded from the Siting
Evaluation Study
Owners/operatorsshouldconsiderlocalenvironmentalconditionsandapplicablebuildingcodeswhenselecting,
constructing,andmaintainingthesetents.Thesetentsshouldbesitedconsistentwiththesitessafework
practices. Owners/operators may consider the following potential
hazards when siting these tents: Proximity to flares, vent stacks,
and atmospheric relief valves. Proximity to sewers and
vents.Proximity to fire and toxic exposures.Proximity to cranes,
heavy lift activities, and vehicle traffic.
Obstructionstoescaperoutesbytentcomponents(e.g.,guywiresshouldbemarked/flaggedtomitigate
potential tripping hazard).COMMITTEE DRAFT14API RECOMMENDED
PRACTICE 756 5.7Personnel Performing Tent Siting
EvaluationSitingoftentsisanimportanttaskandrequiresappropriateconsiderationoftechnicaldataregardingthe
performanceoftentswhenexposedtoexplosions,fires,ortoxicreleases.
Whilesimplemethodsareavailablein
thisdocumenttoestablishstandoffdistances,theimportanceofsitingtentsrequiresthatdecisionsbemadeby
appropriate,qualifiedpersonnel.
Someoptionsforperformingdetailedanalysisforthesitingoftentscaninvolve
specializedanalysistools.
Owners/operatorsshallevaluatethequalificationsofpersonnelperformingthese
analysesandassignqualifiedpersonnelaccordingly.
Further,owners/operatorsshallestablishpolicyregarding approval
requirements and responsibilities for tent siting evaluation.
5.8Management of Tent Occupancy Owners/operators shall develop
policies and practices to control the use of tents by personnel.
Consideration should be given to locating nonessential personnel as
far as practicable from the hazard and discouraging congregation of
personnel in tents close to process areas.Owner/operators should
periodically confirm that tents are being used as intended, and the
tent siting should be re-evaluated if the intended use changes.
Tents should be removed from the site when no longer needed.
5.9Implementation and Change
ControlThisrecommendedpracticeprovidesinformationthatcanbeusedwhenestablishingorupdatingpoliciesor
procedures concerning the placement of tents.Specific tent siting
guidelines and procedures for managing change shall be developed
for the use and location of tents. Examples of changes that should
be managed include: Changes to plant operations, processes or
equipment (including decommissions or additions)that cause a
changeinthepotentialfor,orseverityof,explosion,fire,ortoxicimpactsatthelocationofthetent.In
particular, when a tent is sited using the alternative work process
(described in 5.3) or when a unit that was shutdown is brought back
online. Addition of a new tent to the facility. A modification or
addition to an existing tent occurs that could cause a change in
the impact from explosion, fire, or toxic material release. A
change in the occupancy status or function of a tent. If a tent
sited using the alternative work process is used for different
application. If a tent is relocated.If the number of personnel or
time spent inside the tent increases either permanently or for a
defined period of time. COMMITTEE DRAFTMANAGEMENT OF HAZARDS
ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS15 5.10Documentation
Owners/operators shall document the following elements of the
siting evaluation: Assessment approach (see 5.2 or 5.3); Scenario
selection basis (see 5.2.4); Analysis methodologies (see Sections
6, 7, and 8); Applicability of analysis methodologies; Data sources
used in the analysis;Applicability of data sources; Tent siting
evaluation criteria (see 5.2.1); and Results of the analysis for
tents included in the tent siting evaluation study. Where specific
features e.g. heating, ventilation or air conditioning (HVAC),
blast resistance, gas detection system, and/or safety instrumented
systems] are used to meet the siting evaluation criteria, the
performance and/or design
requirementsshallbedocumented.Thespecificfeaturesaboveshallbemonitoredandmaintainedoverthelife
cycle of the tent. Where procedures are used to meet the
sitingevaluation criteria, it shall be verified that they are
implemented, effective, and in continuous use while the tent is in
use. 6Tent Siting Evaluation for Explosion 6.1Siting and Design of
Tents for Explosions Tents included in the tent siting evaluation
study shall be sited and designed to meet the owner/operators tent
siting evaluation criteria for explosions.6.2Work Process
OverviewThis work process is applicable to those tents that are
included in the tent siting evaluation study using the general tent
siting evaluation process described in 5.2, and is shown in Figure
7. Owners/operators shall determine if the tent could be impacted
by explosion. Where no potential explosion scenario
isidentifiedwhichcouldadverselyaffectthetentunderconsideration,asitingevaluationforexplosionisnot
required; however the analysis and conclusion shall be
documented.COMMITTEE DRAFT16API RECOMMENDED PRACTICE 756 Figure
7.Work Process: Tent Siting Evaluation for Explosion
TheworkprocessforexplosionevaluationisidenticaltothatdescribedinSection6ofAPIRP-752,withthe
following differences: 1.The analysis may account for the reduced
explosion potential of process areas that are shut down and
de-inventoried for the entire time the tent is occupied. (see B.1.4
in API-753 for an example) 2.Structural analysis methods specific
to tents are utilized (see 6.4). 3.Tent testing may be used in lieu
of structural analysis (see 6.5). COMMITTEE DRAFTMANAGEMENT OF
HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS17 6.3Tent
Siting Methodology This methodology will provide reasonable
assurance that the tent will survive potential blast overpressures
and the
tentoccupantswillnotbeseriouslyinjured.Themethodinvolvescalculatingthecongestedvolumeofadjacent
process areas and applying Figure 8 to determine suitable standoff
distances. Figure 8.Tent Siting/Design Guidancefor Explosion
Hazards The tent siting methodologyuses the same zone concept as
API-RP 753, with the only difference being that Figure 8 covers
only explosion hazards (whereas API RP-753 uses a comparable figure
to provide minimum siting criteria for explosions, fire, and
toxics). Tent siting is based on the tents blast capacity.Generic
blast capacities for scaffold structures (see Figure 2) have not
been established by this RP because there is too much variety in
the choice of structural materials, connections, fabric, and
construction to specify a generic blast rating.Siting of scaffold
structures should be evaluated on a case-by-case basis using a
detailed analysis. Generic blast capacities for other types of
tents have been established based on data in REF XXX (BakerRisk
Paper on Tent Testing).It is not currently possible to develop a
generic Pressure-Impulse curve for tents due to the wide
variability of tent construction and lack of sufficient test and
analytical data, but it is possible to establish conservative
generic blast capacities for tents.Based on the currentlyavailable
data, tents (other than scaffold structures) may be sited using the
following criteria: Any tent may be used in Zone 3 without any
blast or structural analysis.This includes tension membrane tents,
pole and light frame tents, non-wind-rated tents, and tents with no
sides.Tents located in Zone 1 or Zone 2 require a blast analysis to
predict the blast overpressure and impulse at the tent location.See
API RP-752 Section 6.3 to determine VCE blast loads. oAny tent may
be sited at a location where the predicted blast overpressure is
less than or equal to 0.6 psi.COMMITTEE DRAFT18API RECOMMENDED
PRACTICE 756 oPole tents designed to withstand wind loads of at
least 90 mph, light frame tents designed to withstand wind loads of
at least 90 mph, or any tent with no sides may be sited at a
location where the blast overpressure is equal to or less than 0.9
psi and the impulse is less than 80 psi-ms.oAt any location where
the calculated blast pressure is greater than 0.9 psi or the
impulse is greater 80 psi-ms, the tents blast capacity shall be
established based on 6.4 or 6.5 below. oTents that have rigid
panels require a detailed analysis. Tents located in Zone 1 shall
only be occupied by essential personnel. 6.4Detailed Structural
Analysis
Adetailedstructuralanalysisusesappropriatedynamicanalysismethodstoassesstheresponseofstructural
components(skinorfabric,supportingropesorframingmembers,postsorpoles,tie-downs,etc.)tothepotential
blast loads. As part of the detailed structural analysis process,
structural response criteria for the components shall be
established. The criteria for metallic or wood components are
discussed in various references [References 4, 5, and 6].The
response of fabrics and ropes to blast is highly dependent on the
specific materials used.For example, the elongation prior to
breaking of a nylon rope is significantly greater thanthat for a
Dacron rope.Tent response may vary depending on orientation to
blast. EN 13782 [Reference 7] provides guidance on the analysis and
design of tents subjected to environmental loads. Annex A provides
supplemental guidance to EN 13782 for the analysis and design of
tents subjected to blast loads. 6.5Explosion Testing Testing maybe
usedinlieu oforinadditiontodetailed structuralanalysisto establish
the responseof the tent to blast loading. Both the overpressure and
the impulse of the explosion should be representative of the blast
load at the tent location. 6.6Measures to Reduce Occupant
Vulnerability from Explosions
Explosiontestingontentsandtentcomponentshavedemonstratedthatthetentstructureandfabriccanmove
abruptly in response to the blast loads.Objects struck by the
fabric could be thrown and become a debris hazard.NFPA 5000
(Section 32.2.5.4) and many local building/fire codes that cover
tents specify that the interior perimeter (e.g., 3 ft width) be
open/clear for egress purposes. Keeping the interior perimeter
clear will also reduce the injury potential from the tents response
to a blast load.Personnel and unanchored objects should not be
located within 3 feet from the interior edge of the tent facing the
blast. SeeREF YYY (BakerRisk Paper on Tent Debris Hazards) for more
information.
Strongblastwavescantoppleordisplacelargegroundlevelequipment(vendingmachines,tallshelves,food
preparation equipment, etc.). Such objects should be adequately
secured to prevent tent occupant injury.Sudden tent displacement in
response to the blast may cause attached overhead items such as
lights, and HVAC equipment to fall. Overhead equipment should be
secured or supported to prevent this injury potential. Other
measures which may reduce occupant vulnerability to explosion
include:
Ensuringthetentisassembledandmaintainedinaccordancewiththemanufacturersrecommendations
and local building codes. Particular attention should be paid to
connections. Evaluating and considering the location and the number
of exits to provide appropriate emergency egress. Providing egress
and escape paths away from potential explosion sources. COMMITTEE
DRAFTMANAGEMENT OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS
PLANT TENTS19 7Tent Siting Evaluation for Fire 7.1Siting and Design
of Tents for Fire Tents included in the tent siting evaluation
study shall be sited and designed to meet the owner/operators tent
siting evaluation criteria for fire.7.2Work Process
Owners/operatorsshalldetermineifthetentincludedinthetentsitingevaluationstudycouldbeimpactedby
flammablevaporreleaseorthermalradiation.Inmostcases,tentsarenotsuitableforshelterfromafire.The
primaryfocuswhenaddressingexternalfirescenariosisontentegressandevacuation.Owners/operatorsshall
provide sufficient separation from the fire hazards to allow tent
occupants to escape
safely.Wherenopotentialfirescenariofromprocessareasorequipmentisidentifiedthatcouldadverselyaffectthetent
underconsideration,asitingevaluationforfireisnotrequired;howevertheanalysisandconclusionshallbe
documented. See Figure 9 for a depiction of the tent siting
evaluation for fire hazards work process. COMMITTEE DRAFT20API
RECOMMENDED PRACTICE 756 Figure 9.Work Process: Tent Siting
Evaluation for Fire
TheworkprocessforfireevaluationissimilartothatdescribedinAPIRP-752Section7,withthefollowing
differences:
1.Theanalysismayaccountforthereducedfirepotentialwithprocessareasthatareshutdownandde-inventoried
for the entire time the tent is occupied. 2.Tents are more
vulnerable to fire exposure than permanent buildings and may have
additional fire hazards (see 7.4)Radiant heat may ignite, melt or
soften the tent fabric materials and may potentially release toxic
fumes or drip hot material on personnel.
3.Occupantsinsidetentsmaybemorevulnerabletoflashfiresfromexpandingburningvaporcloudsthanoccupants
inside buildings. 4.The shelter-in-place option cannot be chosen.
COMMITTEE DRAFTMANAGEMENT OF HAZARDS ASSOCIATED WITH LOCATION OF
PROCESS PLANT TENTS21 The ability to safely evacuate in a fire
scenario can be determined by using a spacing tables approach (see
7.3) or through detailed analysis (see 7.4).Section 8 provides
guidance if tent egress and area evacuation is required. 7.3Spacing
Table ApproachWhen a spacing table approach is used, tent siting
for fire hazards is assumed to be adequate for evacuation when the
separation distance in the spacing table is met or exceeded.
7.4Detailed Analysis 7.4.1Determining the Fire Effects at Tent
Location Modeling may be used to predict the effects and durations
of fires attent locations. See API RP-752Section 7 for discussion
on fire modeling. 7.4.2Occupant Vulnerability from Fire Tent
occupant vulnerability from fire may result from any of the
following effects: Temperature rise within the tent. Ingress and
ignition of flammable material.Ingress of smoke and fumes.
Radiantheatthatmayignite,meltorsoftenthetentfabricmaterials,whichmaypotentiallyreleasetoxic
fumes.
Thermalradiationthataffectsevacuatingoccupants(seeAPI521foreffectsofthermalradiationon
personnel). 7.5Egress and Evacuation for Fire Evacuation for fire
includes both egress from the tent and evacuation to a designated
assembly area in accordance with the owner/operators emergency
response plans.The assessment of safe egress from a tent included
in the tent siting evaluation study should consider the amount of
time available to evacuate, the number of occupants in the tent,
the number of exits, and location of exits away from the fire
source. The tent may initially shield occupants from thermal
radiation associated with external fires, allowing time for tent
egress and emergency response. The assessment of safe evacuation
should consider the evacuation route/distance, the fire thermal
flux and duration, and the total number of people involved in the
evacuation. 7.5.1Emergency Response Features Owners/operators
should provide the following emergency response features for
egress/evacuation from tents: Means to warn occupants of the
presence of a flammable release or fire. Emergency action
procedures and training that will facilitate evacuation. COMMITTEE
DRAFT22API RECOMMENDED PRACTICE 756 Emergency exits and safe
evacuation routes adequate for an orderly evacuation of the
occupants. Exits should be directed away from potential fire
sources. Evacuation plan that directs personnel to a designated
assembly area, considering the number of personnel evacuating. Plan
to account for tent occupants at the assembly location. PPE as
necessary for potential exposure to fire scenarios. Fire
extinguishers, when required.
Firemitigationmeasures(e.g.radiationshieldingorwatersprays/delugesystem)toprotectpersonnel
using escape routes. 8Tent Siting Evaluation for Toxic Material
Release8.1Siting and Design of Tents for Toxic Material Release
Tents included in the tent siting evaluation study (and included in
the siting evaluation) shall be sited and designed to meet the
owner/operators tent siting evaluation criteria for toxic material
release.8.2Work Process Owners/operators shall determine if the
tent included in the tent siting evaluation study could be impacted
by a toxic
materialrelease.Wherenopotentialtoxicmaterialreleasescenarioisidentifiedthatcouldadverselyaffectthe
occupants of the tent under consideration, a siting evaluation for
toxic material release is not required;, however the analysis and
conclusion shall be documented. The work process for toxic material
release evaluation is identical to that described in Section 8 of
API RP-752 with the following differences: 1.The analysis may
account for the reduction in potential toxic material releases when
process areas are shut down and de-inventoried for the entire time
the tent is occupied.
2.Inmostcases,tentsarenotsuitableforshelter-in-place.Specializedtentsmaybeusedforshelter-in-place,
but the design requirements for these are not covered by this RP.
The toxic material release evaluation work process involves
determining whether the tent occupants will be impacted by releases
(see 8.3) and if so, providing suitable egress and evacuation (see
8.4).See Figure 10 for the work process for tent siting evaluation
for toxic release. COMMITTEE DRAFTMANAGEMENT OF HAZARDS ASSOCIATED
WITH LOCATION OF PROCESS PLANT TENTS23 Figure 10.Work Process: Tent
Siting Evaluation for Toxic Release 8.3Determining Toxic Impacts on
Tent Occupants
Theowner/operatormayassumethatalltentsincludedinthetentsitingevaluationstudycanbeimpactedby
releases of toxic materials or they may choose to carry out toxic
gas dispersion modeling for eachtent included in the tent siting
evaluation study in order to determine if there is an impact. See
API RP-752Section 8if toxic gas dispersion modeling is to be used
in that assessment. Occupant vulnerability from toxic material
depends onthe dose (concentration of thechemical and durationofthe
exposure) inside the tent and/or during escape.A tent may initially
shield occupants, providing a finite period of time
toenactprotectionmeasuressuchasshutdownofventilationsystems(ifapplicable),sealingofopenings,or
donningofPPE.Occupantvulnerabilityfromexposuretotoxicmaterialscanbeestimatedbasedonthe
concentration of toxic material that infiltrates thetent and the
associated exposure time. The rate of infiltration will COMMITTEE
DRAFT24API RECOMMENDED PRACTICE 756 vary withthe tent
design.Traditional tents and tents with large openings will have a
high infiltration rate, whereas specialized tents may be designed
to have low infiltration rates. 8.4Egress and Evacuation for Toxic
Material Release Evacuation for toxic material release includes
both egress from the tent and evacuation to a designated assembly
area in accordance with owner/operators emergency response
plans.The assessment of safe egress from a tent included in the
tent siting evaluation study should consider the amount of time
available to evacuate, the number of occupants in the tent, and the
number of exits. The assessment of safe evacuation should consider
the evacuation route/distance and the total number of people
involved in the evacuation. When the evacuation for toxic material
release concept ischosen, owners/operators should provide the
following emergency response features for each tent included in the
tent siting evaluation study: Means to warn occupants of the
presence of a toxic material release. Emergency action procedures
and training that will facilitate evacuation. Emergency exits and
safe evacuation routes adequate for an orderly evacuation of the
occupants.Evacuationplanthatdirectspersonneltoadesignatedshelter-in-placeorspecifiedassemblyarea
considering the number of personnel evacuating. Plan to account for
occupants at the assembly area. PPE as necessary for potential
exposure to the toxic release scenario. COMMITTEE DRAFTMANAGEMENT
OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS25 Annex
A (Normative) Structural Analysis for Tents and Other Soft Sided
Structures This method of analyses may be used to determine the
appropriate location for a tent or other soft-sided structure in
the absence of test data, as discussed in 6.34. Structural analyses
of tents should be performed as prescribed in European Standard EN
13782-2005 [Reference 7]
butmodifiedbytheadditionsandexceptionsdescribedinthisannex.Eachsub-sectionheadinginthisannex
containsareferencetothepertinentparagraphnumberfromtheENStandard.Thisannexdescribeshowthe
procedure prescribed in the corresponding paragraph of the EN
Standard is modified to conduct a structural analysis of a tent.
A.1 Wind Loads (Refer to EN Standard 6.4.2) The local jurisdiction
wind loads may be used in place of the wind loads identified in
this section of the EN Standard.If no local requirements are in
force for tents and other soft-sided structures, the provisions in
this section should be used. A.2. Fundamental combinations (Refer
to EN Standard 6.6.2) The partial safety factor,F,is 1.0 for blast
loads. A.3Blast Loads (Additional Section) (Refer to EN Standard
6.7) The loading of a flexible structure such as a tent is more
complex than for typical buildings in that the response of
thetentfabricmaybefastenoughtoaltertheappliedpressures.Tentsmayallowtheblastwavetopropagate
through the fabric as well as leak through openings and reduce the
net load on the tent. Structural analyses may be performed to
evaluate the response of the tent at its proposed location under
three different loading cases: (1) Rigid Body Loading, (2)
Windward-Leeward Loading, and (3) Blast Transmission through the
Tent.
Thosethreeloadingcasesareintendedtoboundtheactualloadingsthatmayoccuronthetentenvelopeand
frame.The time of application of the load for each panel of the
structure should be based on the time required for the blastwave to
reach the midpoint of the panel.The cases are intended to bound
theactualloadings that may
occuronthetentenvelopeandframe.Ifdynamicfluidstructureinteractioncalculationsthataccountforfabric
movement or test are performed, the results of those calculations
may be used in lieu of the prescribed load cases.Test data that
captures the reduced pressure may also be used in lieu of the
loading cases below, provided the test conditions are
representative of the expected service conditions. Case 1 Rigid
Body Loading This case represents the loading that the sides and
roof panels of the tent would receive if it were a typical
building.Itdoesnotaccountforairleakageorpressureloadingtransmittedthroughthetents.Thereflectedpressureand
impulseswillbeappliedtothesidesandroofpanelsfacingthesourceoftheblast.Theappropriatereflection
COMMITTEE DRAFT26API RECOMMENDED PRACTICE 756
factorsthataccountforboththeincidentoverpressureandtheangleofincidenceareavailablefromtheASCE
[Reference 4] and other sources. The incident overpressure will be
applied to the back of the structure and to the roof panels either
facing away from or parallel to the direction of the blast. Figure
A 1.Load Pattern for Case 1 Loading (Blast Source to the Left) Case
2 Windward-Leeward Loading This case represents the load
distribution that results from the blast wave loading the structure
in a manner similar to
normalwindloads.Thereflectedpressureandimpulseswillbeappliedtothesidesandroofpanelsfacingthe
source of the blast.The appropriate reflection factors that account
for both the incident overpressure and the angle of incidence are
available from the ASCE [Reference 4] and other sources. The
incident overpressure will be applied to the back of the structure
and to the roof panels either facing away from
orparalleltothedirectionoftheblast,butasoutwardpressurestocapturetheeffectoftheblastwavemoving
through the structure. Figure A 2.Load Pattern for Case 2 Loading
(Blast Source to the Left) COMMITTEE DRAFTMANAGEMENT OF HAZARDS
ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS27 Case 3 Blast
Transmission through the Tent This case represents the loading
thatwill result if the blastwave enters the tent and attempts to
blowout the roof and back (and side) walls.The reflected pressure
and impulses will be applied to the sides facing the source of the
blast.The appropriate reflection factors that account for both the
incident overpressure and the angle of incidence are available from
the ASCE [Reference 4] and other sources.
Theincidentoverpressurewillbeappliedtothebackofthestructureandtotheroofpanels,butasoutward
pressures to capture the effect of the blast wave moving through
the structure. Figure A 3.Load Pattern for Case 3 Loading (Blast
Source to the Left) A.4Membrane (Refer to EN Standard 7.5) Tent
fabrics will respond as flexible membranes.The dynamic analysis
shall account for this membrane behavior.Reactions at the edges of
the fabrics are transmitted to the tent structure either through
bearing, or via mechanical connectors.
MembranesmaybeanalyzedwithSingle-Degree-of-Freedom(assumesrigidsupports)orbyamethodthat
considers the flexibility of supports such as Two-Degree-of-Freedom
or Finite Element Analysis. A.5 Verification of load bearing
capacity of technical textiles and their connections (Refer to EN
Standard 7.6)
Wheredynamictestdataisavailable,DynamicIncreaseFactors(DIFs)maybeusedtoincreasethedesign
resistance computed in Equation 7 of the EN Standard. A.6 Safety
Margin, Safeguards (Refer to EN Standard 7.7) The framing members
and/or poles of the tent shall be designed to resist the loads
resulting from the fabric reactions for Load Cases 1, 2, and 3.
Framing member response should be limited to the medium level of
response as defined in ASCE [Reference 4]. Frame connectors must be
able to transfer the calculated reactions between components and
remain ductile. The safety factor against overturning, sliding, and
lifting for blast loads is 1.0. COMMITTEE DRAFT28API RECOMMENDED
PRACTICE 756 Bibliography The following documents are directly
referenced in this RP. [1]OSHA, Title 29 Code of Federal
Regulations (CFR) Part 1910.119, Process Safety Management of
Highly Hazardous Chemicals [2]Dows Fire & Explosion Index
Hazard Classification Guide, Wiley-American Institute of Chemical
Engineers (AIChE)[3]Imperial Chemical Industries, The Mond Index,
ICI PLC, Explosion Hazards Section, Technical Department,
Winnington, UK, 1985 [4]Design of Blast Resistant Buildings in
Petrochemical Facilities, American Society of Civil Engineers
(ASCE) [5]PIP STC01018, Process Industry Practice, Blast Resistant
Building Design Criteria, 2006 [6]PDC Technical Report 06-08,
Single Degree of Freedom Structural Response Limits for
Antiterrorism Design, U.S. Army Corps of Engineers Protective
Design Center, October 2006 [7]Temporary Structures - Tents
Safety,BS EN 13782 12/23/05 [8]Life Safety Code, NFPA 101
[9]Standard for Grandstands, Folding and Telescopic Seating, Tents,
and Membrane Structures, NFPA 102 [10]DOE Standard 1088-95 [11]NFPA
5000, Building Structure and Safety Code, 2012, National Fire
Protection Association [12]BakerRisk paper on Tent Debris Hazards
Further ReadingThe following documents are not directly referenced
in this RP but may provide a useful source of information.
GeneralReferences Not Specific to Particular Subject Area
Guidelines for Postrelease Mitigation in the Chemical Process
Industry, Center for Chemical Process Safety (CCPS) Lees Loss
Prevention in the Process Industries: Hazard Identification,
Assessment and Control, Third Edition, 2004 Tent Siting Evaluation
Process M. H. Goose, Location and design of occupied buildings at
chemical plantsassessment step by step, Hazards XV, The Process,
its Safety, and the Environment, Getting it Right, April 4 to 6,
2000, Manchester, (IChem E Symposium Series No. 147, pp. 461 to
476) Guidance for the Location and Design of Occupied Buildings on
Chemical Manufacturing Sites, Chemical Industries Association (CIA)
Guidelines for Evaluating Process Plant Buildings for External
Explosions, Fires and Toxics, Second Edition, Center for Chemical
Process Safety (CCPS) (work in progress)COMMITTEE DRAFTMANAGEMENT
OF HAZARDS ASSOCIATED WITH LOCATION OF PROCESS PLANT TENTS29 Risk
and Risk Criteria Approved methods and algorithms for DOD
explosives siting, Department of Defense Explosives Safety Board
Technical Paper No. 14, Alexandria, Virginia, November 2008
Guidelines for Developing Quantitative Safety Risk Tolerance
Criteria, Center for Chemical Process Safety (CCPS), 2009 PGS 3:
Guidelines for quantitative risk assessment, TNO (the Purple Book),
formerly CPR 18 (3.5 MB PDF) IN ENGLISH PGS 4: Methods for
determining and processing probabilities, TNO (the Red Book),
formerly CPR 12E, (1.4 MB PDF) IN ENGLISH Guidelines for Chemical
Process Quantitative Risk AnalysisSecond Edition, Center for
Chemical Process Safety (CCPS), Wiley-American Institute of
Chemical Engineers (AIChE), 1999 M. Moosemiller, Avoiding Pitfalls
in Assembling and Equipment Failure Rate Database for Risk
Assessments, Journal of Hazardous Materials, 130 (2006) pp. 128 to
132 Spouge, J., New Generic Leak Frequencies for Process Equipment,
Process Safety Progress, December 2005 Occupant Vulnerability
Methods for the Determination of Possible Damage to People and
Objects Resulting from Releases of Hazardous Materials, TNO Green
Book, CPR 16E, The Hague, Netherlands, 1992 Fire and Explosion PGS
2: Methods for the calculation of physical effects, due to releases
of hazardous materials (liquids and gases), TNO (the Yellow book),
formerly CPR 14E (3.3 MB PDF) Guidelines for Evaluating the
Characteristics of Vapor Cloud Explosions, Flash Fires, and BLEVES,
Center for Chemical Process Safety (CCPS), Wiley-American Institute
of Chemical Engineers (AIChE) Harris and Wickens, Understanding
Vapour Cloud ExplosionsAn Experimental Study, British Gas PLC,
Communication 1408, 1989 Causes and Effects of Fires and
Explosions, FM Global Property Loss Prevention Data Sheet 7-0 2006.
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