Trenching Safety (M026)

Trenching Safety

TRENCHING SAFETYINTRODUCTION TO TRENCHING HAZARDS

Infrastructure Health & Safety Association5110 Creekbank Road, Suite 400, Mississauga, Ontario L4W 0A1 Canada1-800-263-5024 www.ihsa.ca

The contents contained in this publication are for general information only. This publication should not beregarded or relied upon as a definitive guide to government regulations or to safety practices andprocedures. The contents of this publication were, to the best of our knowledge, current at the time ofprinting. However, no representations of any kind are made with regard to the accuracy, completeness, orsufficiency of the contents. The appropriate regulations and statutes should be consulted. Readers shouldnot act on the information contained herein without seeking specific independent legal advice on theirspecific circumstance. The Infrastructure Health & Safety Association is pleased to answer individualrequests for counselling and advice.

© Infrastructure Health & Safety Association, 1991

All rights reserved. This publication may not be reproduced, in whole or in part, or stored in any material form,without the express written permission of the copyright owner.

Revised, December 2007Revised, January 2009Revised, November 2010

ISBN-13: 978-0-919465-50-3

w w w. i h s a . c a INFRASTRUCTURE HEALTH & SAFETY ASSOCIAT ION 3

BACKGROUND

Contents•Background

•Soil types

•Causes of cave-ins

•Protection against cave-ins

•Other hazards and safeguards

•Emergency procedures

•Appendix A: The “Excavations” part of theConstruction Regulation (O. Reg. 213/91)

•Review Quiz

BackgroundFatalities

A significant number of deaths and injuries insewer and watermain work are directly relatedto trenching.

Trenching fatalities are mainly caused by cave-ins. Death occurs by suffocation orcrushing when a worker is buried by falling soil.

Over half of all powerline contacts involve buriedcable. Before excavating, the gas, electrical, andother services in the area must be accuratelylocated and marked. If the service poses ahazard, it must be shut off and disconnected.

Injuries

The following are the main causes of lost-timeinjuries in the sewer and watermain industry:

• materials and equipment falling into thetrench

• slips and falls as workers climb on and offequipment

• unloading pipe

• handling and placing frames and coversfor manholes and catch basins

• handling and placing pipe and othermaterials

• being struck by moving equipment

• falls as workers climb in or out of anexcavation

• falling over equipment or excavatedmaterial

• falling into the trench

• exposure to toxic, irritating, or flammablegases.

Many of these injuries are directly related totrenching.

Regulations

Supervisors and workers in the sewer andwatermain industry must be familiar with the“Excavations” section of the ConstructionRegulation, reprinted in Appendix A of thismanual.

It is important to understand, for instance, theterms “trench” and “excavation.” An excavationis a hole left in the ground as the result ofremoving material. A trench is an excavation inwhich the depth exceeds the width (Figure 1).

The “Excavations” section of the ConstructionRegulation identifies the various types of soilsand specifies the type of shoring and timberingto be used for each. It also spells out therequirements for trench support systems thatmust be designed by a professional engineer.

Difference between excavation and trench

Figure 1

Excavation Trench10'

5'

10'

5'

4 INFRASTRUCTURE HEALTH & SAFETY ASSOCIAT ION w w w. i h s a . c a

SOIL TYPES

Soil typesThe type of soil determines the strength andstability of trench walls.

Identifying soil types requires knowledge, skill,and experience. Even hard soil may containfaults in seams or layers that make it unstablewhen excavated.

The foreman or supervisor must beknowledgeable about soil types found on aproject and plan protection accordingly. Thisknowledge must include an awareness that soiltypes and conditions can change over very shortdistances. It is not unusual for soil to changecompletely within 50 metres or for soil tobecome saturated with moisture over evensmaller distances.

The Construction Regulation sets out four soiltypes. If you are unsure about the soil type,have the soil tested to confirm the type.

Type 1 — It is hard to drive a pick into Type 1soil. Hence, it is often described as “hardground to dig”. In fact, the material is so hard, itis close to rock.

When excavated, the sides of the excavationappear smooth and shiny. The sides will remainvertical with no water released from the trenchwall.

If exposed to sunlight for several days, the wallsof Type 1 soil will lose their shiny appearancebut remain intact without cracking andcrumbling.

If exposed to rain or wet weather, Type 1 soilmay break down along the edges of theexcavation.

Typical Type 1 soils include “hardpan,”consolidated clay, and some glacial tills.

Type 2 — A pick can be driven into Type 2soil relatively easily. It can easily be excavatedby a backhoe or hand-excavated with somedifficulty.

In Type 2 soil, the sides of a trench will remainvertical for a short period of time (perhapsseveral hours) with no apparent tension cracks.However, if the walls are left exposed to air andsunlight, tension cracks will appear as the soilstarts to dry. The soil will begin cracking andsplaying into the trench.

Typical Type 2 soils are silty clay and less densetills.

Type 3 — Much of the Type 3 soil encounteredin construction is previously excavated material.Type 3 soil can be excavated without difficultyusing a hydraulic backhoe.

When dry, Type 3 soil will flow through fingersand form a conical pile on the ground. DryType 3 soil will not stand vertically and thesides of the excavation will cave in to a naturalslope of about 1 to 1 depending on moisture.

Wet Type 3 soil will yield water when vibratedby hand. When wet, this soil will stand verticallyfor a short period. It dries quickly, however,with the vibration during excavation causingchunks or solid slabs to slide into the trench.

All backfilled or previously disturbed materialshould be treated as Type 3. Other typical Type3 soil includes sand, granular materials, and siltyor wet clays.

Type 4 — Type 4 soil can be excavated withno difficulty using a hydraulic backhoe. Thematerial will flow very easily and must besupported and contained to be excavated to anysignificant depth.

With its high moisture content, Type 4 soil isvery sensitive to vibration and otherdisturbances which cause the material to flow.

Typical Type 4 material includes muskeg orother organic deposits with high moisturecontent, quicksand, silty clays with highmoisture content, and leta clays. Leta clays arevery sensitive to disturbance of any kind.


CAUSES OF CAVE-INS

Causes of Cave-InsSoil properties often vary widely from the top tothe bottom and along the length of a trench.

Many factors such as cracks, water, vibration,weather, and previous excavation can affecttrench stability (Figure 2). Time is also a criticalfactor. Some trenches will remain open for along period, then suddenly collapse for noapparent reason.

Figure 3 shows the typical causes of cave-ins.

The main factors affecting trench stability aresoil type, moisture, vibration, surcharge,previous excavation, existing foundations, andweather.

Moisture content

The amount of moisture in the soil has a greateffect on soil strength.

Once a trench is dug, the sides of the openexcavation are exposed to the air. Moisturecontent of the soil begins to change almostimmediately and the strength of the walls maybe affected.

The longer an excavation is open to the air, thegreater the risk of a cave-in.

Trench open for extended duration may collapse without apparent reason.

Equipment vibrationaffects stability.

Backfill isless stable thanundisturbed soil.

Surcharge such as spoil pile puts more pressure on trench walls.

Figure 3

Large Load

Rain

Insufficient ShoringVibration

Cracks

Broken Line High Water TableWater Seepage

Settling

Figure 2 - Many factors affect trench stability.


CAUSES OF CAVE-INS

Vibration

Vibration from various sources can affect trenchstability.

Often trench walls are subject to vibration fromvehicular traffic or from construction operationssuch as earth moving, compaction, pile driving,and blasting. These can all contribute to thecollapse of trench walls.

Surcharge

A surcharge is an excessive load or weight thatcan affect trench stability.

For instance, excavated soil piled next to thetrench can exert pressure on the walls.Placement of spoil piles is therefore important.Spoil should be kept as far as is practical fromthe edge of the trench. Mobile equipment andother material stored close to the trench alsoadd a surcharge that will affect trench stability.

One metre from the edge to the toe of the spoilpile is the minimum distance requirement(Figure 4). The distance should be greater fordeeper trenches.

Previous excavation

Old utility trenches either crossing or runningparallel to the new trench can affect the strengthand stability (Figure 5).

Soil around and between these old excavationscan be very unstable. At best it is consideredType 3 soil — loose, soft, and low in internal

strength. In some unusual circumstances it maybe Type 4 — wet, muddy, and unable tosupport itself.

This kind of soil will not stand up unless it issloped or shored.

Existing foundations

Around most trenches and excavations there is afailure zone where surcharges, changes in soilcondition, or other disruptions can causecollapse.

When the foundation of a building adjacent tothe trench or excavation extends into this failurezone, the result can be a cave-in (Figure 6). Soilin this situation is usually considered Type 3.

Weather

Rain, melting snow, thawing earth, and overflowfrom adjacent streams, storm drains, and sewersall produce changes in soil conditions. In fact,water from any source can reduce soil cohesion(Figure 7).

Existing foundations are surrounded bybackfill and may add a surcharge load to the pressure on the trench wall.

Figure 6

Move spoil pile farther back for deep trenches

Figure 4

Old utilities are surrounded by backfilled soil which is usually less stable than undisturbed soil.

Figure 5

1m 1m 1m


PROTECTION AGAINST CAVE-INS

Frozen soil does not mean that you can havereduced shoring or that a heavier load can besupported. Frost extends to a limited depth only.

Protection AgainstCave-InsThere are three basic methods of protectingworkers against trench cave-ins:

• sloping

• trench boxes

• shoring

Most fatal cave-ins occur on small jobs of shortduration such as service connections andexcavations for drains and wells. Too oftenpeople think that these jobs are not hazardousenough to require safeguards against collapse.

Unless the walls are solid rock, never enter atrench deeper than 1.2 metres (4 feet) if it is notproperly sloped, shored, or protected by atrench box.

Sloping

One way to ensure that a trench will notcollapse is to slope the walls.

Where space and other requirements permitsloping, the angle of slope depends on soilconditions (Figures 8, 9 and 10).

For Type 1 and 2 soils, cut trench walls back atan angle of 1 to 1 (45 degrees). That's onemetre back for each metre up. Walls should besloped to within 1.2 metres (4 feet) of thetrench bottom (Figure 8).

For Type 3 soil, cut walls back at a gradient of 1to 1 from the trench bottom (Figure 9).

For Type 4 soil, slope the walls at 1 to 3. That’s3 metres back for every 1 metre up from thetrench bottom (Figure 10).

Although sloping can reduce the risk of a cave-in,the angle must be sufficient to prevent spoil notonly from sliding back but also from exerting toomuch pressure on the trench wall (Figure 11).

Sloping is commonly used with shoring ortrench boxes to cut back any soil above theprotected zone. It is also good practice to cut abench at the top of the shoring or trench(Figure 12).

Moisture affects stability, especially where heavy rainfall has occurred

Figure 7

GOOD SOIL Type 1 & 2 Soil

MinimumBank SlopeMaximum

1.2 m (4 ft.)

Figure 8

Figure 10

Figure 9

FAIRLY GOOD SOIL Type 3 Soil

MinimumBank Slope

BAD SOIL Type 4 Soil

MinimumBank Slope

Spoil piles can exert too much pressure on sloped trench wall.

Figure 11



If sloping is to be used above a trench box, thetop portion of the cut should first be sloped 1 to1 (or 1 to 3 for Type 4 soil — see previouspage). Then the box should be lowered into thetrench (Figure 13).

Trench boxes

Trench boxes are not usually intended to shoreup or otherwise support trench walls. They aremeant to protect workers in case of a cave-in.

Design drawings and specifications for trenchboxes must be signed and sealed by theprofessional engineer who designed the systemand must be kept on site by the constructor.

Boxes are normally placed in an excavated butunshored trench and used to protect personnel.A properly designed trench box is capable ofwithstanding the maximum lateral load expectedat a given depth in a particular soil condition.

Trenches near utilities, streets, and buildingsmay require a shoring system.

As long as workers are in the trench theyshould remain inside the box. Workers must notbe inside the trench or the box when the box isbeing moved. A ladder must be set up in thetrench box at all times.

Excavation should be done so that the spacebetween the trench box and the excavation isminimized (Figure 14).

The two reasons for this are

1) allowing closer access to the top of thebox

2) limiting soil movement in case of a cave-in.

Check the drawings and specifications for thetrench box to see if the space between the boxand the trench wall needs to be backfilled andthe soil compacted.

Shoring

Shoring is a system which “shores” up orsupports trench walls to prevent movement ofsoil, underground utilities, roadways, andfoundations.

Shoring should not be confused with trenchboxes. A trench box provides worker safety butgives little or no support to trench walls orexisting structures such as foundations andmanholes.

The two types of shoring most commonly usedare timber and hydraulic. Both consist of posts,wales, struts, and sheathing.

Figures 15 and 16 identify components,dimensions, and other requirements for timbershoring in some typical trenches.

Keep space between trench box and excavation as small as possible.

Backfill if necessary to prevent acave-in.

Figure 14

Cut back unshored top position with a 1 to 1 slope(or a 1 to 3 slope for Type 4 soil)

Figure 13

Figure 12

It is good practice to cut abench at top of shoring



“Hydraulic shoring” refers to prefabricated strutand/or wale systems in aluminum or steel. Strictlyspeaking, these may not operate hydraulically.Some are air-operated or manually jacked. Designdrawings and specifications for prefabricatedshoring systems must be kept on site.

One major advantage of hydraulic shoring oversome applications of timber shoring is safetyduring installation. Workers do not have to enterthe trench to install the system. Installation canbe done from the top of the trench.

Most hydraulic systems are

• light enough to be installed by one worker

• gauge-regulated to ensure even distributionof pressure along the trench line

• able to “pre-load” trench walls, therebyusing the soil's natural cohesion to preventmovement.

• easily adapted to suit various trench depthsand widths.

Wherever possible, shoring should be installedas excavation proceeds. If there is a delaybetween digging and shoring, no one must beallowed to enter the unprotected trench.

All shoring should be installed from the topdown and removed from the bottom up.

Access/egress

Whether protected by sloping, boxes, or shoring,trenches must be provided with ladders so thatworkers can enter and exit safely (Figure 17).

Ladders must

• be placed within the area protected by theshoring or trench box

• be securely tied off at the top

• extend above the shoring or box by atleast 1 metre (3 feet)

Figure 15

Figure 16

Ladders shouldbe placed withinshored area andtied off to preventslipping.

Figure 17



• be inspected regularly for damage.

Ladders should be placed as close as possible tothe area where personnel are working andnever more than 7.5 metres (25 feet) away.

Anyone climbing up or down must always facethe ladder and maintain 3-point contact. Thismeans that two hands and one foot or two feetand one hand must be on the ladder at alltimes.

Maintaining 3-point contact also means handsmust be free for climbing. Tools and materialsshould not be carried up or down ladders. Pumps,small compactors, and other equipment should belifted and lowered by methods that prevent injuryfrom overexertion and falling objects.

Inspection

Inspection is every one's responsibility. Whateverthe protective system, it should be inspectedregularly.

Check hydraulic shoring for leaks in hoses andcylinders, bent bases, broken or crackednipples, and other damaged or defective parts(Figure 18).

Check timber shoring before installation. Discarddamaged or defective lumber. After installation,inspect wales for signs of crushing. Crushingindicates structural inadequacy and calls formore struts (Figure 19).

Inspect trench boxes for structural damage,cracks in welds, and other defects (Figure 20).During use, check the box regularly and oftento make sure that it is not shifting or settlingmuch more on one side than the other. If it is,leave the trench and ask the supervisor to checkfor stability.

Check ground surface for tension cracks whichmay develop parallel to the trench at a distanceone-half to three-quarters of the trench depth(Figure 21). If cracks are detected, alert the crewand check all protective systems carefully.

Check areas adjacent to shoring where watermay have entered the trench. A combination ofwater flow and granular soils can lead toundermining of the trench wall. Such conditionshave caused fatalities.

Finally, make sure that tools, equipment,material, and spoil are kept at least 1 metre (3 feet) back from the edge of the trench toprevent falling objects from striking workers.

Check hydraulicshoring

for leaks.

Figure 18

Cracked sheathing

Inspect walesfor crushing at struts. Strut off level

Bowed sheathingand wales

Loose ormissingcleats

Figure 19


OTHER HAZARDS AND SAFEGUARDS

Summary

Sloping, trench boxes, and shoring are meant toprotect workers from the hazards of cave-ins.

The method chosen must meet the specificrequirements of the job at hand. Depending onapplication, one method may be better suited tocertain conditions than another.

Whatever the system, inspect it regularly tomake sure that it remains sound and reliable.

Remember: Never enter a trench more than1.2 metres (4 feet) deep unless it is sloped,shored, or protected by a trench box.

Other Hazards andSafeguardsThe risk of a cave-in is not the only hazard intrenching. Injuries and deaths are also related tosix other major areas:

• personal protective equipment

• utilities underground and overhead

• materials handling and housekeeping

• heavy equipment

• traffic control

• confined spaces.

Personal protective equipment

Personal protective equipment is an importantdefence against certain types of injury.

Injuries from falling and flying objects, forinstance, can be reduced by wearing hard hatsand eye protection.

Everyone on a construction project must wearGrade 1 safety boots certified by the CanadianStandards Association (CSA) as indicated by theCSA logo on a green triangular patch (Figure 22).

Under the wet, muddy conditions oftenencountered in trenching, you may also requirerubber safety boots displaying the same CSAlogo on a green triangular patch.

Deformed PlateCheck welds on

sleeves and strutsfor bends

and distortion

Damage

BentStrut

MissingStrut

Figure 20

Sidewall

Check fortension cracks Strut

Knife edge

Figure 21



It is mandatory for everyone on a constructionproject to wear head protection in the form of ahard hat that complies with the currentConstruction Regulation.

Eye protection is strongly recommended toprevent injuries from construction operationssuch as chipping and drilling and site conditionssuch as dust.

Personnel exposed for long periods to noisyequipment should wear hearing protection.

Work in confined spaces such as manholes andvalve chambers may require respiratoryprotection against hazardous atmospheres. See“Confined Spaces” in this manual for moreinformation.

See IHSA’s Construction Health and SafetyManual (M029) for more information onpersonal protective equipment.

Underground utilities

Locates — Services such as gas, electrical,telephone, and water lines must be located bythe utility before excavation begins.

Request locates for all the underground utilitiesin the area where excavation will be takingplace. The contractor responsible for the workmust contact the owners of any undergroundutilities that may be in that location or phone

Ontario One Call (1-800-400-2255). Someutilities are not part of the Ontario One Callsystem. Contact those utilities separately forlocate requests.

The service locate provided by the utility ownershould indicate, using labelled stakes, flags,and/or paint marks, the centre line of theunderground utility in the vicinity of theproposed excavation.

The excavator should not work outside of thearea covered by the locate stakeout informationwithout obtaining an additional stakeout.

Locate stakeout accuracy should be consideredto be 1 metre on either side of the surfacecentre line locate unless the locate instructionsspecifically indicate other boundary limits.

Where the underground utility cannot belocated within the locate stakeout limits, theutility owner should be contacted to assist withthe locate.

Figure 22 Existing utility lines may require support.

Figure 23

Figure 24

Have existingutilities locatedbeforeexcavating.



Mechanical excavation equipment should not beused within the boundary limits of the locatewithout first digging a hole or holes using theprocedure below to determine the undergroundutility's exact centre line and elevation.

Test holes should, in general, be excavated byone of the following methods:

(a) machine excavation immediately outsidethe boundary limits and then hand digginglaterally until the underground utility isfound; or

(b) (i) hand excavation perpendicular tothe centre line of the locate in cuts of atleast 1 foot in depth;

(ii) mechanical equipment can then beused carefully to widen the hand-dugtrench to within one foot of the depthof the hand-dug excavation;

(iii) repeat steps (i) and (ii) until theutility is located; or

(c) a hydro-excavation system — acceptableto the owner of the utility — which useshigh-pressure water to break up the covermaterial and a vacuum system to remove itcan be used to locate the undergroundutility. See the next section for moreinformation about hydro excavation.

Centre line locates should be provided and testholes dug where a representative of the utilityidentifies

(a) alignment changes

(b) changes in elevation.

Where an underground utility may need supportor where it may shift because of disturbance ofsurrounding soil due to excavation, guidelinesfor excavation and support should be obtainedfrom the owner of the utility (Figure 23).

Hydro excavation —

Precautions:

• Before starting work, use barricades andsigns to inform unauthorized personnel tokeep out.

• Employers must ensure that workers areproperly trained on the machine they areusing.

• When exposing underground powerutilities the operators should use bondingmats.

• Use a fall-protection system whenrequired.

• Keep clear of the vacuum. It is powerfuland can cause serious injury or even deathif you are caught in the tube.

• Some utility owners set limits for the waterpressure that can be used near their buriedplan. Check with the utility owner beforeexcavating.

• Excavators can refer to the following forfurther information:

- TSSA/ESA Guidelines for Excavations inthe Vicinity of Gas Lines

- Safe Practice Guide Excavating withHydrovacs in the Vicinity of Underground Electrical Plant, available from IHSA (www.ihsa.ca).

Workers using or in the vicinity of hydroexcavation:

Services shouldbe exposed firstby hand digging,then by machine.

Figure 25



• Keep away from the operation if you arenot directly involved in the work.

• Wear hearing protection if working invicinity of the hydrovac truck.

• Be aware of the hazards, such as slipsfrom the runoff water and ice during thewinter.

• Wear appropriate eye and face protectionsuch as safety glasses and faceshields.They will protect you from getting anyairbourne debris (caused by splashing) inyour eyes.

• Keep clear of the vacuum. It is powerfuland can cause serious injury or even deathif you are caught in the tube.

Breaks — Breaks in electrical, gas, and waterservices can cause serious injuries, even deaths.Hitting an underground electrical line can resultin electrocution, while hitting a gas line cancause an explosion. A broken water line canrelease a sudden rush of water, washing outsupport systems and causing a cave-in.

Cutting telephone lines can create a seriousproblem if emergency calls for police, fire, orambulance are required.

In the event of gas line contact, call the gascompany immediately. The company will checkthe line and close down the supply if necessary.

If a leak is suspected, people in the immediatearea should be told to evacuate. Where service toa building or home has been struck, peopleinside should be advised to leave doors andwindows open; shut off appliances, furnaces, andother sources of ignition; and vacate the premisesuntil the gas company declares it safe to return.

Construction personnel should take twoprecautions.

1)Put out smoking materials and shut offother sources of ignition such as enginesand equipment.

2) Leave the trench immediately. Gas cancollect there.

Overhead powerlines

When equipment operates within reach of (andcould therefore encroach on) the minimumpermitted distance from a live overhead powerline,the constructor must have written procedures inplace to prevent the equipment from encroachingon the minimum distance.

If equipment touches a high-voltage line,the operator should take the followingprecautions.

1) Stay on the machine. Don’t touchequipment and ground at same time.Touching anything in contact with theground could be fatal.

2)Anyone operating accessory equipmentshould also remain on that equipment.They should also avoid making contactwith the ground and the equipment at thesame time.

Voltage Rating of Powerline Minimum Distance

750 or more volts, but not 3 metres (10')more than 150,000 volts

more than 150,000 but 4.5 metres (15')not more than 250,000 volts

more than 250,000 volts 6 metres (20')

Keep people away from machineif there is a powerline contact.

Stay on the machine unless thereis an emergency such as fire.

Figure 26



3)Keep others away. Warn them not to touchthe load, load lines, boom, bucket, or anyother part of the equipment (Figure 26).

4)Get someone to call the local utility to shutoff power.

5) If possible, the operator (while remainingon the machine) can try to break contactby moving the machine clear of the wires.

Warning: Beware of time relays. Evenafter breakers are tripped by linedamage, relays may be triggered torestore power.

6) If the operator can’t break contact bymoving the machine (while remaining onit), do not move the machine until theutility shuts down the line and confirmsthat power is off.

7) If an emergency such as fire forces you toleave the machine, jump clear (Figure 27).Never step down. If part of your bodycontacts the ground while another parttouches the machine, current will travelthrough you.

8) Jump with feet together and shuffle awayin small steps. Don’t take big steps. Withvoltage differential across the ground, onefoot may be in a higher voltage area thanthe other. The difference can kill you(Figure 28).

Special precautions are required for casualties incontact with live powerlines or equipment.

1)Never touch the casualty or anything incontact with the casualty.

2) If possible, break contact. Use a dry board,rubber hose, or dry polypropylene rope tomove either the casualty or the line. Anobject can sometimes be thrown toseparate the casualty from the wire.

Warning : Touching the casualty, evenwith dry wood or rubber, can bedangerous. With high voltage lines,objects that are normally insulatorscan become conductors.

3)Call emergency services — in most casesambulance, fire department, and utility.

Voltage differentialacross the ground caninjure or kill you.

Figure 28

If an emergency forces you to leave the machine, jump clear with feet together and shuffle away — never step down.

Figure 27



4)Provide first aid once the casualty is free ofcontact. If the casualty is not breathing,begin artificial respiration immediately(mouth-to-mouth is most efficient) or CPR.Apply cold water to burns and cover withclean dressing.

Materials handling

Many lost-time injuries in trenching involvematerials handling. Moving rock and soil, liftingpipe and manhole sections, laying downbedding material, or lowering pumps andcompactors into the trench can all be hazardous.

Pipe — Trucks should always be on level

ground when pipe is unloaded. Pipe should be

chocked or staked before tie-downs are

released. These measures will reduce the risk of

sections rolling off the truck.

Plastic and small diameter pipe is often bandedwith metal straps. Be careful cutting the straps.They are under tension and can fly back and hityou.

Personnel often injure fingers and hands whenlaying and joining sections of pipe. While sections

are suspended from hoisting equipment, keephands away from slings or chokers in tension.When guiding and pushing sections together byhand, never curl fingers around ends or flanges.

As pipe is placed along the trench, each sectionshould be blocked or set so that it cannot rolland cause injury.

Back injuries can occur when small-diameterpipe is being homed into position (Figure 29).The worker pushing the bar should place hisfeet directly in front of the pipe with one footahead of the other.

Large-diameter pipe should be placed with pipepullers (Figure 30).

Bedding material — Personnel shovellingbedding material in the trench are usuallyworking in a confined area where footing ismuddy and uneven.

The result can be overexertion or slips and fallsleading to back and other injuries. Mechanicalequipment can significantly reduce this hazard.For instance, bedding material can be put in theexcavator bucket with a front-end loader, thenspread evenly along the trench bottom.

Rigging — Rigging is essential to safe, efficientmaterials handling since pipe, manhole sections,and equipment are lowered into the trench bycranes or other hoisting devices.

Rigging these loads properly can prevent injury.

Inspect slings and rigging hardware regularlyand replace any damaged or worn devices.

With nylon web slings, damage is usuallyeasy to spot: cuts, holes, tears, worn or distortedfittings, frayed material, broken stitching, heat

Figure 30

To maintainbalance, keepone foot aheadof the other.

Figure 29



burns. Damaged web slings should be replaced.

When using wire rope slings, inspect forbroken wires, worn or cracked fittings, looseseizings and splices, flatening, and corrosion.Knots or kinks indicate that wire rope slings arepermanently damaged and should not be used.

Damage most often occurs around thimbles andfittings. Don't leave wire rope lying on theground for any length of time in damp or wetconditions.

Eyes in wire rope slings should be fitted withthimbles. To make an eye with clips, put the U-bolt section on thedead or short end ofthe rope and thesaddle on the live orlong end (Figure 31).Remember — neversaddle a dead horse.

At least three clips arerequired for wire ropeup to 5/8" diameter,and four are requiredfor wire rope greaterthan 5/8" up to andincluding 7/8"diameter.

Avoid binding the eyesection of wire ropeslings around corners.The bend will weakenthe splice or swaging.

When using chokerhitches, do not forcethe eye down towardsthe load once tensionis applied.

When using chain slings, inspect for elongatedlinks. A badly stretched link tends to close up(Figure 32).

Look for bent, twisted, or damaged links thatcan result when chain has been used to lift a

load with unprotected sharp edges.

Inspect for cracks. Although sometimes hard todetect, cracks always indicate that the chainshould be removed from service. Also look forgouges, chips, cuts, dents, peen marks, andcorrosive wear at points where links bear oneach other.

Rigging Tips

• Wherever possible, lower loads onadequate blockage to prevent damage toslings.

• Keep hands away from pinch pointswhen slack is being taken up.

• Stand clear while the load is being liftedand lowered or when slings are beingpulled out from under it.

• Use tag lines to control swinging,swaying, or other unwanted movement ofthe load.

Housekeeping

Accident prevention depends on properhousekeeping at ground level and in the trench.

At the top of the trench, sections of pipe,unused tools and timber, piles of spoil, andother material must be kept at least 1 metre (3 feet) away from the edge.

The slips and falls common on excavationprojects can be reduced by cleaning up scrapand debris. Trenches should also be kept as dryas possible. Pumps may be required.

Proper housekeeping is especially important

Dead end

Live endSTEP 1 - Apply first clip one base width fromdead end of rope. U-bolt is placed over deadend and live end rests in clip saddle. Tightennuts evenly to recommended torque.

STEP 2 - Apply second clip as close to loopas possible. U-bolt is over the dead end.Turn nuts firmly but do not tighten.

STEP 3 - Apply all other clips, spacedequally between the first two. They shouldbe 6-7 rope diameters apart.

STEP 4 - Apply tension and tighten all nutsto recommended torque.

STEP 5 - Check nut torque after rope hasbeen in operation.

ApplyTension

ApplyTension

Figure 31

New link

Stretchedlink

Figure 32



around ladders. The base and foot of the laddershould be free of garbage and puddles. Laddersshould be tied off at the top, placed inprotected areas, and inspected regularly fordamage (Figure 33).

Heavy equipment

Excavators, backhoes, and other heavyequipment can cause injuries and fatalities tooperators and personnel on foot.

Excavator handsignals — Communicate

clearly with your co-workers. Use the following

handsignals.

Operators — Improperly climbing on and off

equipment has caused injuries to operators for

many years. The best prevention is to maintain

3-point contact (Figure 34).

Equipment should be fitted with steps, grabs,and rails that are repaired or replaced whendamaged.

Operators have also suffered serious injurieswhen equipment upsets because of soil failurenear excavations (Figure 35), improper loadingon floats, or inadvertently backing intoexcavations.

Use 3-point contacton steps and rails.

Figure 34

Try to push backfill intoexcavation rather thandumping it.

Figure 35

Ladders should be placed within shoredarea and tied off to prevent slipping.

Figure 33



Moving equipment — Signallers are required

by law

• if the operator's view of the intended pathof travel is obstructed, or

• if a person could be endangered by themoving equipment or its load.

Back-up alarms are required on dump trucksand recommended for all moving equipment.Where vehicles have to operate in reverse,warning signs must be conspicuously posted.

Ground rules for truck drivers

• Understand and obey the signaller at alltimes.

• Remain in the cab where possible.

• Ensure that mirrors are clean, functional,and properly adjusted.

• Do a circle check after being away from thetruck for any length of time (walk aroundthe truck to ensure the area is clear beforemoving).

• Stop immediately when a signaller, worker,or anyone else disappears from view.

Workers on foot — Personnel on foot are

frequently stuck by machine attachments such

as excavator buckets and bulldozer blades when

they stand or work too close to operating

equipment, especially during unloading and

excavation.

Workers on foot are also injured and killed byequipment backing up.

Ground rules for workers on foot

• Beware of common operator blind spots. See chapter on Backing Up in this manual.

• Stay alert to the location of equipmentaround you.

• Avoid entering or standing in blind spots.

• Always remain visible to the operator.

Make eye contact to ensure that youare seen.

• Never stand behind a backing vehicle.

• Remember — the operator may be able tosee you while you are standing but notwhen you kneel down or bend over.

Signallers — In heavily travelled or congested

work areas, a signaller may be necessary to

direct equipment and prevent injuries and

deaths caused by vehicles backing up.

Ground rules for signallers

• Wear a fluorescent or bright orangesafety vest.

• Use standard hand signals (Figure 37).

• Stand where you can see and be seen.

• Stay in full view of the operator and theintended path of travel.

• Know where the operator's blind spotsare.

• Warn other workers to stay clear ofequipment.

Traffic control

On trenching projects along public roadways,the construction crew must be protected fromtraffic. Regulations specify the followingmethods for protecting personnel:

Back up

Clearance

ChangeDirection

Stop

Figure 37



• traffic control persons (TCPs) using signs(Figure 38)

• warning signs

• barriers

• lane control devices

• flashing lights or flares.

Supervisors must train TCPs on site and explainthe nature of the project, where constructionequipment will be operating, and how publictraffic will flow. TCPs must wear a fluorescentor bright orange safety vest.

Training must also include the proper use of theSTOP/SLOW sign, where to stand, how tosignal, and communication with other TCPs.(See the chapter on Traffic Control in IHSA’sConstruction Health and Safety Manual (M029).)

After presenting this information, the supervisorsmust give TCPs written instructions in alanguage they can understand.

Confined spaces

A confined space is defined as a place

a) that is partially or fully enclosed

b) that is not both designed and constructedfor continuous human occupancy, and

c) where atmospheric hazards may occurbecause of its construction, location, orcontents, or because of work that is donein it.

All three critera have to be met before a space

is defined as a confined space.

In the sewer and watermain industry, confinedspaces can be locations such as excavations,manholes, valve chambers, pump stations, andcatch basins. The atmosphere in these spacesmay be

• toxic

• oxygen-deficient

• oxygen-enriched

• explosive.

Sewage not only smells bad but can createdangerous atmospheres. Decaying wastereleases hazardous gases such as hydrogensulfide and methane. The bacteria in sewage arenot only a source of infection but can alsoconsume oxygen and leave the atmosphereoxygen-deficient.

Other sources of contamination can include

• fumes from welding or patchingcompounds

• chemicals from waste disposal sites

• engine exhaust

• propane or other explosive gases that areheavier than air and collect in the bottomof the trench

• leaks from underground storage tanks

• decomposing material in landfill sites.

Protecting the health and safety of personnelstarts with some basic steps.

• A competent worker must test a confinedspace to determine whether it is hazard-free before a worker enters, and continuetesting to ensure that it remains hazard-free.

•Where tests indicate safe air quality,workers may be allowed to enter theconfined space.

Figure 38


EMERGENCY PROCEDURES

• Where tests indicate a hazardous level offumes, vapours, gases, or oxygen, entrymust not be allowed until the space hasbeen adequately ventilated and subsequenttests indicate that the air is safe to breathe.

• Where possible, mechanical venting shouldbe continued in any confined spacecontaining hazardous levels of fumes,vapours, gases, or oxygen, even afterventing has corrected the hazard. Thespace must also be continuously monitoredwhile personnel are working there.

• In situations where ventilation hasremoved a hazard, workers entering thespace should still wear rescue harnessesattached to individual lifelines. A workershould also beposted at theentranceprepared,equipped, andtrained toprovide rescuein anemergency. Forrescuesituations,workersentering thespace shouldwear supplied-air respirators(Figure 40).

For more information on confined spaces andcontrols, see the chapter on Confined Spaces inIHSA’s Construction Health and Safety Manual(M029).

Hydrostatic testing

Hydrostatic testing involves entry into a confinedspace such as a manhole or valve chamber. Theprocedures listed above should be followed.

Testing new lines can be very hazardous ifcomponents break or plugs let go. For that

reason, additional precautions are required.

When testing watermains, ensure that all lines,elbows, and valves are supported and equippedwith thrust blocks. Otherwise the line couldcome apart under test pressure.

Arrange watermain testing so that lines arepressurized when no one is in the manhole orvalve chamber.

For sewer line testing, all requirements forentering confined spaces apply.

Ensure that plugs are secure. No one should bein a manhole when the upstream line is beingfilled. Plugs that are not properly installed canlet go, causing injury and letting a manhole fillquickly, depending on the size of the line.

Flooding is another reason why no one shouldbe in a manhole without a rescue harness and aworker outside ready and prepared for anemergency.

Emergency ProceduresGeneral

Emergency telephone numbers — ambulance,fire, police, local utilities, senior management,Ministry of Labour — should be posted in thefield office for quick reference.

If someone is seriously injured, take thefollowing steps.

1)Protect the area from hazards.

2)Prevent further injury to the casualty.

3)Administer first aid.

4)Call an ambulance or rescue unit.

5)Have someone direct the ambulance orrescue unit to the accident scene.

All projects must have a person qualified andcertified to provide first aid.

Cave-ins

It is natural to try to rescue casualties caught or

Self-containedbreathingapparatus(SCBA)

Figure 40


EMERGENCY PROCEDURES

buried by a cave-in. But care must be taken toprevent injury and death to rescuers, whetherfrom a further cave-in or other hazards.

The following procedures may be suitable,depending on conditions.

1)To get down to the casualty, use atarpaulin, fencing, plywood, or similarmaterial that can cover the ground and willride up over any further cave-in.

2) Sometimes a further cave-in can beprevented by placing a backhoe bucketagainst the suspected area or excavating it.

3)Rescue workers should enter the trenchwith ropes and wear rescue harnesses ifpossible.

4)To prevent further injury, remove thecasualty by stretcher whenever possible.Tarps or ladders can be used as amakeshift stretcher.

5) Stabilize the casualty.

Breathing — Ensure that the casualty isbreathing. If not, open the airway and startartificial respiration immediately. Mouth-to-mouth is the most efficient method.

Bleeding — Control external bleeding byapplying direct pressure, placing the casualty ina comfortable position, and elevating the injuredpart if possible.

Unconsciousness — This is a priority becauseit may lead to breathing problems. Anunconscious person may suffocate when leftlying face up. If injuries permit, unconsciouspersons who must be left unattended should be

placed in the recovery position (Figure 41).

Recovery position

Figure 41


APPENDIX A AND REVIEW QUIZ

APPENDIX ATHE “EXCAVATIONS” PART OF THE

CONSTRUCTION REGULATION (ONTARIOREGULATION 213/91)

REVIEW QUIZ


APPENDIX A

Part III ExcavationsInterpretation

222. In this Part,

“engineered support system” means anexcavation or trench shoring system, designed fora specific project or location, assembled in placeand which cannot be moved as a unit;

“hydraulic support system” means a systemcapable of being moved as a unit, designed toresist the earth pressure from the walls of anexcavation by applying a hydraulic counterpressure through the struts;

“prefabricated support system” means a trenchbox, trench shield or similar structure, composedof members connected to each other and capableof being moved as a unit, and designed to resistthe pressure from the walls of an excavation butdoes not include a hydraulic support system;

“pressure”, in relation to a wall of an excavation,means the lateral pressure of the earth on thewall calculated in accordance with generallyaccepted engineering principles and includeshydrostatic pressure and pressure due tosurcharge. O. Reg. 213/91, s. 222.

223. This Part applies to all excavating andtrenching operations. O. Reg. 213/91, s. 223.

Entry and Working Alone

224. No person shall enter or be permitted toenter an excavation that does not comply withthis Part. O. Reg. 213/91, s. 224.

225. Work shall not be performed in a trenchunless another worker is working above groundin close proximity to the trench or to the meansof access to it. O. Reg. 213/91, s. 225.

Soil Types

226. (1) For the purposes of this Part, soil shallbe classified as Type 1, 2, 3 or 4 inaccordance with the descriptions set out inthis section. O. Reg. 213/91, s. 226 (1).

(2) Type 1 soil,

(a) is hard, very dense and only able tobe penetrated with difficulty by asmall sharp object;

(b) has a low natural moisture contentand a high degree of internalstrength;

(c) has no signs of water seepage; and

(d) can be excavated only bymechanical equipment. O. Reg. 213/91, s. 226 (2).

(3) Type 2 soil,

(a) is very stiff, dense and can bepenetrated with moderate difficultyby a small sharp object;

(b) has a low to medium naturalmoisture content and a mediumdegree of internal strength; and

(c) has a damp appearance after it isexcavated. O. Reg. 213/91, s. 226 (3).

(4) Type 3 soil,

(a) is stiff to firm and compact to loosein consistency or is previously-excavated soil;

(b) exhibits signs of surface cracking;

(c) exhibits signs of water seepage;

The “Excavations” part of the ConstructionRegulation (Ontario Regulation 213/91)


APPENDIX A

(d) if it is dry, may run easily into awell-defined conical pile; and

(e) has a low degree of internalstrength. O. Reg. 213/91, s. 226 (4).

(5) Type 4 soil,

(a) is soft to very soft and very loose inconsistency, very sensitive and upondisturbance is significantly reducedin natural strength;

(b) runs easily or flows, unless it iscompletely supported beforeexcavating procedures;

(c) has almost no internal strength;

(d) is wet or muddy; and

(e) exerts substantial fluid pressure on itssupporting system. O. Reg. 213/91, s. 226 (5).

227. (1) The type of soil in which an excavationis made shall be determined by visual andphysical examination of the soil,

(a) at the walls of the excavation; and

(b) within a horizontal distance fromeach wall equal to the depth of theexcavation measured away from theexcavation. O. Reg. 213/91, s. 227 (1).

(2) The soil in which an excavation is madeshall be classified as the type described insection 226 that the soil most closelyresembles. O. Reg. 213/91, s. 227 (2).

(3) If an excavation contains more thanone type of soil, the soil shall be classifiedas the type with the highest number asdescribed in section 226 among the typespresent. O. Reg. 213/91, s. 227 (3).

Precautions Concerning Services

228. (1) Before an excavation is begun,

(a) the employer excavating shall ensure

that all gas, electrical and otherservices in and near the area to beexcavated are located and marked;

(b) the employer and worker locatingand marking the services describedin clause (a) shall ensure that theyare accurately located and marked;and

(c) if a service may pose a hazard, theservice shall be shut off anddisconnected. O. Reg. 443/09, s. 6.

(2) If a service may pose a hazard and itcannot be shut off or disconnected, theowner of the service shall be requested tosupervise the uncovering of the serviceduring the excavation. O. Reg. 443/09, s. 6.

(3) Pipes, conduits and cables for gas,electrical and other services in an excavationshall be supported to prevent their failure orbreakage. O. Reg. 443/09, s. 6.

Protection of Adjacent Structures

229. (1) If an excavation may affect the stabilityof an adjacent building or structure, theconstructor shall take precautions to preventdamage to the adjacent building orstructure. O. Reg. 213/91, s. 229 (1).

(2) A professional engineer shall specify inwriting the precautions required undersubsection (1). O. Reg. 213/91, s. 229 (2).

(3) Such precautions as the professionalengineer specifies shall be taken. O. Reg.213/91, s. 229 (3).

General Requirements

230. Every excavation that a worker may berequired to enter shall be kept reasonablyfree of water. O. Reg. 213/91, s. 230.

231. An excavation in which a worker may workshall have a clear work space of at least 450millimetres between the wall of theexcavation and any formwork or masonry


APPENDIX A

or similar wall. O. Reg. 213/91, s. 231.

232. (1) The walls of an excavation shall bestripped of loose rock or other material thatmay slide, roll or fall upon a worker. O. Reg. 213/91, s. 232 (1).

(2) The walls of an excavation cut in rockshall be supported by rock anchors or wiremesh if support is necessary to prevent thespalling of loose rock. O. Reg. 213/91, s. 232 (2).

233. (1) A level area extending at least onemetre from the upper edge of each wall ofan excavation shall be kept clear ofequipment, excavated soil, rock andconstruction material. O. Reg. 213/91, s. 233 (1).

(2) The stability of a wall of an excavationshall be maintained where it may beaffected by stockpiling excavated soil orrock or construction materials. O. Reg.213/91, s. 233 (2).

(3) No person shall operate a vehicle orother machine and no vehicle or othermachine shall be located in such a way asto affect the stability of a wall of anexcavation. O. Reg. 213/91, s. 233 (3).

(4) If a person could fall into an excavationthat is more than 2.4 metres deep, a barrierat least 1.1 metres high shall be provided atthe top of every wall of the excavation thatis not sloped as described in clauses 234 (2)(e), (f) and (g). O. Reg. 213/91, s. 233 (4).

Note: See subsections 263 (2) and (3) of theCriminal Code of Canada, R.S.C. 1985,Chap. C-46, as amended, with respect to theduty imposed upon persons in charge of anexcavation.

Support Systems

234. (1) The walls of an excavation shall besupported by a support system thatcomplies with sections 235, 236, 237, 238,

239 and 241. O. Reg. 213/91, s. 234 (1).

(2) Subsection (1) does not apply withrespect to an excavation,

(a) that is less than 1.2 metres deep;

(b) that no worker is required to enter;

(c) that is not a trench and with respectto which no worker is required tobe closer to a wall than the height ofthe wall;

(d) that is cut in sound and stable rock;

(e) made in Type 1 or Type 2 soil andwhose walls are sloped to within 1.2metres of its bottom with a slopehaving a minimum gradient of onehorizontal to one vertical;

(f) made in Type 3 soil and whosewalls are sloped from its bottomwith a slope having a minimumgradient of one horizontal to onevertical;

(g) made in Type 4 soil and whosewalls are sloped from its bottomwith a slope having a minimumgradient of three horizontal to onevertical; or

(h) that is not a trench and is not madein Type 4 soil and with respect towhich a professional engineer hasgiven a written opinion that thewalls of the excavation aresufficiently stable that no worker willbe endangered if no support systemis used. O. Reg. 213/91, s. 234 (2).

(3) The opinion in clause (2) (h) shallinclude details of,

(a) the specific project and the locationthereon;

(b) any specific condition for which theopinion applies; and


APPENDIX A

(c) the frequency of inspections. O. Reg. 213/91, s. 234 (3).

(4) The constructor shall keep on theproject a copy of every opinion given by aprofessional engineer for the purpose ofclause (2) (h) while the project is inprogress. O. Reg. 213/91, s. 234 (4).

(5) The professional engineer who gives anopinion described in clause (2) (h), or acompetent worker designated by him orher, shall inspect the excavation to whichthe opinion relates as frequently as theopinion specifies. O. Reg. 213/91, s. 234 (5).

235. (1) Subject to subsection (2), a supportsystem shall consist of,

(a) timbering and shoring that meets therequirements of subsection 238 (2),if no hydrostatic pressure is presentin the soil, and if the width anddepth of the excavation are equal toor less than the width and depthindicated in the Table to section 238;

(b) a prefabricated support system thatcomplies with sections 236 and 237;

(c) a hydraulic support system thatcomplies with sections 236 and 237;or

(d) an engineered support system thatcomplies with section 236. O. Reg. 213/91, s. 235 (1).

(2) Where the excavation is a trench andthe depth exceeds six metres or the widthexceeds 3.6 metres, the support system shallconsist of an engineered support systemdesigned for the specific location andproject. O. Reg. 213/91, s. 235 (2); O. Reg. 631/94, s. 7.

236. (1) Every prefabricated, hydraulic orengineered support system shall bedesigned by a professional engineer. O. Reg. 213/91, s. 236 (1).

(2) Every prefabricated, hydraulic orengineered support system shall beconstructed, installed, used and maintainedin accordance with its design drawings andspecifications. O. Reg. 213/91, s. 236 (2).

(3) The design drawings and specificationsfor a prefabricated, hydraulic or anengineered support system,

(a) shall indicate the size of the systemand the type and grade of materialsof which it is to be made;

(b) shall indicate the maximum depthand the types of soil for which it isdesigned;

(c) shall indicate the proper positioningof the system in the excavation,including the maximum allowableclearance between the walls of thesupport system and the walls of theexcavation; and

(d) shall indicate how to install andremove the system.

(e) REVOKED: O. Reg. 85/04, s. 21. O. Reg. 213/91, s. 236 (3); O. Reg. 85/04, s. 21.

(4) In addition to the requirements ofsubsection (3), the design drawings andspecifications for a hydraulic supportsystem,

(a) shall indicate the minimum workingpressure required for the system;and

(b) shall require the use of a device toensure the protection of workers if aloss of hydraulic pressure occurs inthe system. O. Reg. 213/91, s. 236 (4).

(5) Before a variation from the designdrawings and specifications for aprefabricated, hydraulic or an engineered


APPENDIX A

support system is permitted, the variationshall be approved in writing by a professionalengineer. O. Reg. 213/91, s. 236 (5).

(6) If the soil conditions on a project differfrom those assumed by the professionalengineer in designing a prefabricated,hydraulic or an engineered support system,a professional engineer shall modify thedesign drawings and specifications for theactual soil conditions or shall approve thesupport system for use in the actual soilconditions. O. Reg. 213/91, s. 236 (6).

(7) The constructor shall keep the designdrawings and specifications for aprefabricated, hydraulic or an engineeredsupport system at a project while the systemis on the project. O. Reg. 213/91, s. 236 (7).

(8) REVOKED: O. Reg. 443/09, s. 7.

237. (1) Subject to subsection (2),

(a) no prefabricated or hydraulicsupport system shall be used in type4 soil;

(b) the space between the walls of aprefabricated support system and thewalls of the excavation shall berestricted to the minimum clearancerequired for the forward progressionof the support system; and

(c) the walls of a hydraulic supportsystem shall touch the walls of theexcavation. O. Reg. 631/94, s. 8.

(2) A prefabricated or hydraulic supportsystem may be used for repairingunderground pipe breaks if the system,

(a) meets the requirements of section236;

(b) has four side walls;

(c) is designed for a maximum depth of3.6 metres;

(d) is not used at a greater depth than3.6 metres;

(e) is designed to resist all hydrostaticand earth pressures found in type 3and type 4 soils;

(f) is installed so as to extend to thebottom of the excavation;

(g) is installed so that the walls of thesystem touch the walls of theexcavation; and

(h) is not pulled forward after beinginstalled in the excavation. O. Reg. 631/94, s. 8.

(3) Before a support system is used asdescribed in subsection (2), the constructorshall submit two copies of its designdrawings and specifications to the office ofthe Ministry of Labour nearest to theproject. O. Reg. 631/94, s. 8.

238. (1) In this section,

“cleat” means a member of shoring thatdirectly resists the downward movement ofa wale or strut;

“o/c” means the maximum distancemeasured from the centre of one memberof sheathing, wale or strut to the centre ofthe adjacent member of sheathing, wale orstrut;

“post” means a vertical member of shoringthat acts as a spacer between the wales;

“10 millimetres gap” means that the spacebetween two adjacent members ofsheathing is a maximum of ten millimetres.O. Reg. 213/91, s. 238 (1).

(2) Timbering and shoring referred to inclause 235 (1) (a) for the walls of anexcavation with a depth and located in asoil type described in Column 1 of theTable to this section shall meet thecorresponding specifications set out in


APPENDIX A

Columns 2 to 4 of the Table. O. Reg. 213/91, s. 238 (2).

(3) Every piece of sheathing referred to inthe Table to this section shall be made ofsound Number 1 Grade spruce and,

(a) shall be placed against the side ofthe excavation so that it is vertical;

(b) shall be secured in place by wales;and

(c) shall be driven into the soil andfirmly secured in place if theexcavation is made in Type 3 or 4soil. O. Reg. 213/91, s. 238 (3).

(4) Every strut referred to in the Table tothis section shall be made of sound number1 structural grade spruce and,

(a) shall be placed in the excavation sothat it is horizontal and at rightangles to the wales;

(b) shall be cut to the proper length andheld in place by at least two wedges

driven between the strut and thewales; and

(c) shall be cleated with cleats thatextend over the top of the strut andrest on the wales or that are attachedsecurely to the wales by spikes orbolts. O. Reg. 213/91, s. 238 (4).

(5) Every wale referred to in the Table tothis section shall be made of sound Number1 structural grade spruce and,

(a) shall be placed in the excavation sothat it is parallel to the bottom, orproposed bottom, of the excavation;and

(b) shall be supported by either cleatssecured to the sheathing or posts seton the wale next below it or, if it isthe lowest wale, on the bottom ofthe excavation. O. Reg. 213/91, s. 238 (5).

239. (1) A support system for the walls of anexcavation shall be installed,

EXCAVATION SHORING AND TIMBERING (METRIC SIZES)

Column 1 Column 2 Column 3 Column 4

Excavation

Depth

Soil

TypeSheathing

Struts

WalesWidth of Excavation at Strut Location Strut Spacing

1.8 m to 3.6 m Up to 1.8 m Vertical Horizontal

3.0 m or

less

1 50 mm × 200 mm at 1.2 m o/c 200 mm × 200 mm 150 mm × 150 mm 1.2 m * 2.4 m *200 mm × 200 mm

2 50 mm × 200 mm at 1.2 m o/c 200 mm × 200 mm 150 mm × 150 mm 1.2 m * 2.4 m *200 mm × 200 mm

3 50 mm × 200 mm at 10 mm gap 200 mm × 200 mm 200 mm × 200 mm 1.2 m 2.4 m 250 mm × 250 mm

4 75 mm × 200 mm at 10 mm gap 250 mm × 250 mm 200 mm × 200 mm 1.2 m 2.4 m 300 mm × 300 mm

Over 3.0 m

to 4.5 m

1 50 mm × 200 mm with 10 mm gap 200 mm × 200 mm 150 mm × 150 mm 1.2 m 2.4 m 200 mm × 200 mm



Over 3.0 mto 4.0 m


Over 4.5 m

to 6.0 m




* Note: For excavations to 3 m deep in soil types 1 and 2, the wales can be omitted if the struts are used at 1.2 m horizontal spacings.O. Reg. 213/91, s. 238, Table; O. Reg. 631/94 s. 9.


APPENDIX A

(a) progressively in an excavation inType 1, 2 or 3 soil; and

(b) in advance of an excavation in Type4 soil, if practicable. O. Reg. 213/91,s. 239 (1).

(2) A support system for the walls of anexcavation shall provide continuous supportfor it. O. Reg. 213/91, s. 239 (2).

(3) No support system for the walls of anexcavation shall be removed untilimmediately before the excavation isbackfilled. O. Reg. 213/91, s. 239 (3).

(4) A competent person shall supervise theremoval of a support system for the walls ofan excavation. O. Reg. 213/91, s. 239 (4).

240. If a support system is used for the walls ofan excavation, a ladder for access to oregress from the excavation shall be placedwithin the area protected by the supportsystem. O. Reg. 213/91, s. 240.

241. (1) A support system for the walls of anexcavation shall extend at least 0.3 metresabove the top of the excavation unlessotherwise permitted or required by thissection. O. Reg. 213/91, s. 241 (1).

(2) If an excavation is located where thereis vehicular or pedestrian traffic and if theexcavation will be covered when work onor in it is not in progress, the supportsystem for the walls of the excavation shallextend at least to the top of the excavation.O. Reg. 213/91, s. 241 (2).

(3) If the upper portion of the walls of anexcavation are sloped for the soil types asdescribed in clauses 234 (2) (e), (f) and (g)and the lower portion of the walls arevertical or near vertical, the walls shall besupported by a support system whichextends at least 0.5 metres above thevertical walls. O. Reg. 213/91, s. 241 (3).

242. (1) A metal trench-jack or trench-brace may

be used in place of a timber strut,

(a) if the allowable working load of thetrench-jack or trench-brace is equalto or greater than that of the timberstrut; and

(b) if the size of the replaced timberstrut is shown on the trench-jack ortrench-brace. O. Reg. 213/91, s. 242 (1).

(2) The allowable working load of a metaltrench-jack or trench-brace shall bedetermined by a professional engineer inaccordance with good engineering practiceand shall be legibly cast or stamped on thetrench-jack or trench-brace. O. Reg. 213/91, s. 242 (2).

(3) No metal trench-jack or trench-braceshall be extended beyond the length usedto establish its maximum allowable workingload. O. Reg. 213/91, s. 242 (3).

(4) Every metal trench-jack or trench-brace,when it is used,

(a) shall be placed against the wales insuch a way that the load from thewales is applied axially to thetrench-jack or trench-brace; and

(b) shall be adequately supported sothat it does not move out ofposition. O. Reg. 213/91, s. 242 (4).


REVIEW QUIZ

REVIEW QUIZ

Background

1. Are there regulations which set outrequirements for trenching projects?

Yes ❑ No ❑

2. The major cause of fatalities in the trenchingindustry is ____________________________.

3. List three causes of lost-time injuries in thetrenching industry.

1______________________________________

2______________________________________

3______________________________________

4. Which diagram best illustrates a trench?

Causes of Cave-ins

1. List three causes of cave-ins.

1______________________________________

2______________________________________

3______________________________________

2. List three sources of vibration.

1______________________________________

2______________________________________

3______________________________________

3. Trench wall stability will change as thetrench is exposed to the weather.

True ❑ False ❑

4. Previously excavated soil, such as that foundaround existing utilities or used for backfill,is usually less stable.True ❑ False ❑

5. Surcharge puts additional pressure on trenchwalls.True ❑ False ❑

Protection Against Cave-ins.

1. The basic methods of protecting workersfrom cave-ins are:

______________________________________

______________________________________

______________________________________

______________________________________

______________________________________

______________________________________

______________________________________

2. The angle of slope for trench walls dependson conditions.True ❑ False ❑

3. Which illustration shows the minimumsloping requirements for an unprotectedtrench in good soil contitions?

4. Trench boxes are usually not intended tosupport the trench walls.True ❑ False ❑

5. The major advantage of hydraulic shoring isthat workers can install it without having toenter the trench.True ❑ False ❑

A or B

A B

C


REVIEW QUIZ

6. Dimensions and components of timbershoring change according to soil conditionsand the depth of the trench.

True ❑ False ❑

7. List two components of timber shoring thatshould always be inspected.

1______________________________________

2______________________________________

8. Ladders must be placed within the areaprotected by the shoring or trench box.

True ❑ False ❑

9. What sign on the ground surface next to thetrench would indicate that the trench wall isbecoming less stable?

______________________________________

______________________________________

______________________________________

Other Hazards and Safeguards

1. List three hazards, other than cave-in, thatcan occur on trenching projects.

1______________________________________

2______________________________________

3______________________________________

2. Underground utilities should first be locatedby the utility company, then exposed byhand digging before using excavationequipment.

True ❑ False ❑

3. Workers should stay well back frommachines operating near overheadpowerlines.

True ❑ False ❑

4. What should you do if the machine strikesoverhead powerlines?

a. Operator __________________________________________________________________

______________________________________

______________________________________

b. Worker ____________________________________________________________________

______________________________________

______________________________________

5. What is the main injury likely to resultduring materials handling? ________________

______________________________________

6. Workers on foot may be injured or killed byequipment backing up.

True ❑ False ❑

7. List three ground rules for signallers.

1______________________________________

2______________________________________

3______________________________________

8. List three ground rules for personnelworking near operating vehicles and heavyequipment.

1______________________________________

2______________________________________

3______________________________________

9. Regulations for traffic control require thatTraffic Control Persons (TCPs) be giveninstruction in a language they understand.

True ❑ False ❑

10. A manhole is a confined space.

True ❑ False ❑

About IHSA

IHSA’s vision is the elimination of all workplace injuries, illnesses, and fatalities within our member fi rms.

We engage with our member fi rms, workers, and other stakeholders to help them continuously improve their health and safety performance. We do this by providing effective and innovative sector-specifi c programs, products, and services.

We offer

• Training programs • Consulting services • Health and safety audits • Publications and e-news • Posters and stickers • Reference material • A resource-rich website.

Find out what we can do for you at www.ihsa.ca

Infrastructure Health & Safety Association (IHSA)5110 Creekbank Road, Suite 400

Mississauga, Ontario L4W 0A1 CanadaTel: 1-800-263-5024 • Fax: 905-625-8998

www.ihsa.ca

M026ISBN-13: 978-0-919465-50-3

Documents

Trenching Safety (M026)