Confined Spaces Shafts Tunnels Trenches

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Confined Spaces - Shafts, Tunnels & Trenches

Introduction

This topic relates to the application of the Occupational Health and Safety (Confined Spaces)Regulations to Excavations in the Building and Construction Industry

If you are an employer or an employee in the building and construction industry in Victoria,this publication will help guide you in applying the Occupational Health and Safety (Confined

Spaces) Regulations 1996.

Confined spaces create unique occupational health and safety problems because the hazards

present may not be obvious. Workers from many different occupations and industries may

enter confined spaces to perform work-related tasks unaware of the dangers.

The Confined Spaces regulations have been put in place to protect workers against health

and safety risks associated with entering, working in and exiting confined spaces.

N.B.: Employers and self-employed persons have responsibilities under the

regulations. So do designers, manufacturers, importers and suppliers. People who areself-employed must comply with the regulations as if they were employers.

The regulations, which set out the duties of employers, are accompanied by a Code of

Practice for Confined Spaces. The Code of Practice provides detailed practical guidance onmeeting the regulatory requirements, and you are encouraged to use it to manage and control

risks in confined spaces.

Purpose of this publication

Within the building and constuction industry, excavations such as shafts, tunnels and

trenches, and associated structures, may fit the definition of confined spaces under theRegulations.

Accordingly, this publication will address the following:

excavations under construction such as shafts, tunnels and trenches; and


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The regulations define a "Confined Space"as follows: a space in any vat, tank, pit, pipe,

duct, flue, oven, chimney, silo, reaction vessel, container, receptacle, underground

sewer, shaft, well, trench, tunnel or other similar enclosed or partially enclosedstructure, if the space -

(a) is, or is intended to be, or is likely to be, entered by any person; and

(b) has a limited or restricted means for entry or exit that makes it physically difficult for aperson to enter or exit the space; and

(c) is, or is intended to be, at normal atmospheric pressure while any person is in the space;and

(d) contained, or is intended to contain, or is likely to contain:

(i) an atmosphere that has a harmful level of any contaminant; or

(ii) an atmosphere that does not have a safe oxygen level; or(iii) any stored substance, except liquids, that could cause engulfment.

How Do I Apply The Definition?

Consider the criteria listed above. If aand band c, and any of dapply, then the space is aconfined space and the regulations apply.

Often, when you apply the criteria it is obvious that an excavation is a confined space.

However, there may be some instances where it is not that easy to decide.

If you are dealing with an excavation that does not fall within the regulatory definition of a

confined space, then the provisions of the Occupational Health and Safety Act 1985 apply.

Appendix 1 provides examples of excavations that do meet and don't meet the definition.

What do the regulations require of employers?

If you are an employer, the regulations require you to manage and control risks that are

associated with confined spaces. Listed below are some of the specific things you must do:

Hazard identification:First, you must properly identify confined spaces by applying the

definition. Then, in consultation with a health and safety representative, you must identify the

hazards that are associated with entering and working in such spaces.

Risk assessment:Next, you must assess the risks to workers who might have to enter the

space. This means you need to determine whether there is any risk, i.e., injury or illness,associated with each of the hazards identified. What is more, you must record and retain the

assessment.


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However, there are specific measures you are required to undertake to control risksassociated with work in a confined space; for example:

you must ensure that a procedure is in place to make it known when any

employee enters or exits a confined space;you must establish effective emergency procedures and ensure that they

are rehearsed; and

you must see to it that the relevant employees are provided withinformation, instruction and training.

Are there specific risk controls I should know about?

Yes, there are a number of risk control measures specific to trenches, shafts, tunnels andassociated construction. Here are some examples:

Isolation of plant and services:You should eliminate any substance or condition that can

be introduced from a plant or by services that are connected to the space. If elimination is not

practicable, you should reduce the risks as far as is practicable.

Ventilation:You may need to install ventilation by mechanical means to make and maintain a

safe atmosphere. The ventilation should be operating long enough to make the atmosphere

safe before any person enters the tunnel. It must also operate continuously when any personis in the excavation.

A fresh air blower or extractor of adequate capacity should be in place before work is startedon any excavation that is defined as a confined space. The ventilation line should be as close

to the working face as is practicable.

Any exhaust emissions from petrol or diesel-driven plant should be vented outside the

confined space in such a way that they cannot contaminate the air in the confined space or

contaminate air being supplied to the space.

Although many shafts and tunnels may not be defined as a confined space, some of these

shafts and most tunnels will require ventilation to remove contaminants from the air, reducethe humidity and maintain a minimum level of 19.5% of oxygen in the atmosphere. It is good

practice to provide ventilation for all small dimensional tunnels longer than 600 mm even if

they are not defined as a confined space.

Ventilation by mechanical means may not be required in many shallow trenches or shallow

shafts (i.e. less than 1.5 metres deep), unless there is a likelihood of unacceptable levels ofharmful atmospheric contaminants or an unsafe level of oxygen. You should carry out

atmospheric testing and a risk assessment to determine if ventilation or other measures are

needed in shallow excavations in contaminated ground or when a live pipe is being cut into.


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What are some of the hazards that I need to look for?

The building and construction industry involves a lot of excavation work, and there are somespecific hazards associated with confined spaces that you need to be aware of. Here are

some examples:

seepage and build-up of gases and liquids from adjacent plant,

installations, service lines or processes;

flammable gases or vapours from sewerage or from the use of solvents;too little or too much oxygen in sewers;

exposure to biological hazards such as leptospirosis and Escherichia coli

(E coli) in sewers;harmful levels of atmospheric contaminants from welding, sewerage or

using solvents with PVC piping;

build-up of harmful levels of exhaust gases, including carbon monoxidefrom plant being used in or close to the space;

seepage and build-up of natural contaminants from ground water and gases

from the surrounding land, soil or strata;displacement of oxygen by other gases in sewers;

too little or too much oxygen caused by processes such as oxy-cutting;

noise;excessively hot or cold working conditions; and

traffic hazards.Entries and exits need special attention:When it comes to tunnels, shafts and trenches, a

major safety factor is having entry and exit openings that are large enough for a properly

equipped person to pass through. The size and number of openings also have an impact on

the degree of natural ventilation.

There are several steps you can take to address these problems. For example:

Make entry and exit openings to the confined space large enough to allow people to enter

wearing any necessary protective clothing and equipment and to permit rescue of all who

may enter the confined space;If there are fixed ladders, platforms, or walkways leading to a confined space, make sure

that these allow safe and easy access. Additional guidance on such access can be found

in AS 1657 Fixed Platforms, Walkways, Stairways and Ladders - Design, Constructionand Installation.

Make sure that there are an appropriate number of properly spaced entry and exit

openings along the length of large, long spaces such as gas pipelines, because these willaffect the degree of natural ventilation and the ease with which a person can be rescued;

Similarly, pay close attention to the ease of entry, exit and passage when the confined

space extends over a significant length or height, as in the case of sewers, pipes,


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1. The following examples fit the regulatory definition of a confined space because each of these spacesis likely to be entered, has a limited means for entry or exit, is at normal atmospheric pressure and is

likely to contain a contaminated atmosphere or unsafe oxygen level.

a. Examples of excavations with harmful contaminants that are confined spaces:

Trenches, shafts, tunnels, manholes, pits, sewer lines, underground pump stations or similar

constructions connected to:

either an open sewer line, a previously live sewer line or a line which is to be opened

or found to be broken or leaking; orany other service line likely to generate a harmful level of any contaminant.

Steel water mains or similar pipelines where:

welding, cutting or other operations are carried out inside the pipeline that are likely either

to create a harmful level of contaminant or deplete oxygen in the atmosphere to an unsafe level.

Shafts or tunnels being excavated to repair, replace or break into any live or previously live sewer line.b. Examples of excavations that have to be assessed on a case by case basis:

Excavations where:

there is no sewer, stormwater, or gas line either exposed or open, or likely to be exposed

or opened, but where there may be leaking service lines nearby, harmful gases from

decomposed material, or other sources being released from the ground itself; orthe presence of engine exhaust gases or the use of solvents or other materials in the

excavation may create a hazardous atmosphere.

Stormwater drains, water mains, pits or similar excavations where there is:

a likehood of either a contaminant entering and contaminating the atmosphere or a

depletion of oxygen (for example, in unused sections of large water mains, or anindustrial area where large quantities of chemicals or other contaminants are being

manufactured or are in use).

Any pit or tunnel that:

has not been connected to a live service line but is sealed from natural

ventilation; orwhere solvents have been in use for sealing pipes and a hazardous

atmosphere may have built up; or

where the curing of fresh concrete may have reduced the oxygen level tobelow 19.5%.

Shallow open shafts and trenches where:

there may only be a small quantity of contaminant in the atmosphere, for example, some

household

connections to live sewer points, and where there may be good natural ventilation.


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Occupational Health and Safety Act 1985apply where a space does not

fall within the regulatory definition of a confined space.

In relation to engulfment, the inclusion of the term "stored material" in the regulatorydefinition is intended to exclude specific trench hazards that are already covered by theSafety Precautions in Trenching Operations Code of Practice. "Stored material" does

not include material that may accumulate as a result of fretting, collapse or exfoliation.

Appendix 2

This appendix has been provided as .GIF image file attachments. To view the images simply

click on the associated icon.NOTE:The files are reasonably large and may take some time to download.


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Appendix 3

Air Quality and Air Testing

Exposure standards represent airborne concentrations of substances which, according to

current knowledge, should neither impair the health of, nor cause undue discomfort to, nearlyall workers.

Substance TWA (ppm) STEL (ppm)

ammonia 25 35

carbon dioxide 5,000 30,000

carbon monoxide 30 100formaldehyde 1 2

hydrogen sulphide 10 15

nitric oxide 25 -nitrogen dioxide 3 5

sulphur dioxide 2 5

Airborne Particulates (dusts)

silica (respirable) 0.2mg/m3 -

inspirable dusts(* measured as inspirable dust)

10mg/m3*

TWA: Time Weighted Average concentration of airborne contaminant over an entire eight-

hour working day, for a five-day working week.STEL: Short-term Exposure Limit concentration of airborne contaminant, averaged over a

period of 15 minutes that should not be exceeded at any time during a work-day evenif theeight-hour TWA average is within the TWA exposure standard. Exposure at the STEL should

not be longer than 15 minutes and should not be repeated more than four times a day. Thereshould be at least 60 minutes between successive exposures at the STEL.

Lower Explosive Limit (LEL)Substance LEL% 5% LEL

methane 5.0* 0.25*

petrol/diesel 1.3* 0.065*

(* the above LELs are examples only; refer to specific material safety data sheet).

Appendix 4


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Appendix 5

Information on Some Additional Hazards

1. Tunnel Collapse

The nature of the space may contribute to the risks associated with hazards present in aconfined space. In carrying out a risk assessment on a tunnel under construction that is also a

confined space, you should consider the soundness, construction and structure of the space.

You should provide appropriate ground support to prevent the tunnel from collapse.

An example of appropriate ground support for a small dimensional tunnel would be to have alltimber ground support, including sets and horizontal lagging, with a minimum of 150 mm x 38

mm F8 hardwood with tunnel sets at a maximum of 1.0 metre centres.

If the tunnel set centres are greater than 1 metre, the dimensions of all supports should be

increased accordingly. In very unstable ground conditions, the set and lagging sizes should

be increased or the set centres decreased to suit the ground conditions.

Steel sets and/or closed timber sheeting may be required in larger dimensional tunnels in

unstable clay or fill material, or when intersecting or adjacent service lines are encountered.

In stable rock conditions, each tunnel entrance from the shaft should be supported with a

minimum of two sets, preferably steel, with additional support provided as necessary.

In all cases, the amount of overhead cover and any additional loadings such as machinery,

traffic, adjacent buildings and intersecting services should be taken into account.

2. Lighting

Where necessary, you should provide either fixed or portable lighting to ensure that the

tunneller can both work safely and also be visible at all times to the stand-by person.

Fixed lighting should be in accordance with the Code of Practice Temporary ElectricalInstallations on Building and Construction Sites. Intrinsically safe lighting should be provided ifexplosive gases are present or are likely to be present in the excavation.

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Confined Spaces Shafts Tunnels Trenches