Common Hazards Associated with Confined Spaces

    What hazards are associated with a confined space?

    Restricted entry or exit

    Small entrances and exits make it difficult to rescue injured workers or to get equipment in or out of the confined space. In some cases, entrances and exits may be very large but their location can make them difficult to access. For example, accessing pits or openings high up in silos may require the use of ladders, hoists or other devices, and escape and rescue from such spaces may be difficult in emergency situations.

    Harmful airborne contaminants

    The following table illustrates the kinds of harmful atmospheres that may be present in a confined space, and how they may be created.

    Source of Contaminant

    • Substance stored in the confined space or its by- product(s)

    Examples

    • release of toxic substances e.g. hydrogen sulphide in tanks of decomposing organic material, especially when the material is disturbed
    • build-up of hydrogen sulphide in sewers and pits
    • Work performed in the confined space
    • use of paints, adhesives, solvents or cleaning solutions
    • welding or brazing with metals capable of producing toxic vapours or gases
    • exhaust vapours or gases from engines used in the confined space
    • painting or moulding glass-reinforced plastics
    • Entry of natural contaminants, e.g. groundwater and gases, into the confined space from the surrounding land, soil or strata
    • acid groundwater acting on limestone with the potential to produce dangerous accumulations of carbon dioxide
    • methane released from groundwater and from decay of organic matter
    • Release of airborne contaminants
    • when sludge, slurry or other deposits are disturbed or when scale is removed
    • Manufacturing process
    • residues left in tanks, vessels etc or remaining on internal surfaces can evaporate into a vapour or gas
    • Entry and accumulation of gases and liquids from adjacent plant, installations, services or processes
    • the contamination of underground confined spaces by substances from plant in the vicinity of the confined space
    • carbon monoxide from the exhaust of LPG-powered forklifts operating in, or in the vicinity of, the confined space

    Unsafe Oxygen Levels

    Air normally contains 21 per cent oxygen by volume, although oxygen levels of 19.5 per cent to 23.5 per cent by volume are considered to be safe.

    Some situations can cause the level of oxygen to dramatically decrease, leading to an oxygen-deficient atmosphere and possible asphyxiation. This may occur if oxygen in the atmosphere is:

    • displaced by gases produced during biological processes, for example methane in a sewer;

    • displaced during purging of a confined space with an inert gas to remove flammable or toxic vapours or gases;

    • depleted inside metal tanks and vessels through surface oxidation (for example when rust forms);

    • consumed during combustion of flammable substances; or,

    • absorbed or reacts with grains, wood chips, soil or chemicals in sealed silos.

    Too much oxygen can increase the risk of fire or explosion. Oxygen-enriched atmospheres may occur if:

    • chemical reactions cause the production of oxygen, for example certain reactions with hydrogen peroxide; or,

    • there is a leak of oxygen from an oxygen tank or fitting while using oxy-acetylene equipment.

    Refer to AS 1674 (Series)1: Safety in welding and allied processes to cover circumstances where ignition source is cutting, grinding or welding.

    Fire and Explosion

    A fire or explosion requires the presence of three elements:

    • an ignition source;
    • air; and,
    • a fuel (gas, vapour or mist) capable of igniting.

    A flammable atmosphere is one in which the flammable gas, vapour or mist is likely to exceed 5 per cent of its lower explosive limit (LEL).

    Flammable atmospheres in confined spaces may result from the evaporation of a flammable residue, flammable materials used in the space, a chemical reaction (such as the formation of methane in sewers), or from the presence of combustible dust (such as that in flour and other grain silos and coal handling areas).

    If an ignition source, such as a sparking electrical tool or static on a person, is introduced into a space containing a flammable atmosphere, an explosion is likely to result.

    Engulfment

    Engulfment means to be swallowed up in or immersed by material, which may result in asphyxiation. Examples of materials that may pose a risk of engulfment include plastics, sand, liquids, fertiliser, grain, coal, coal products, fly ash, animal feed and sewage.

    Stored materials such as sand and grain can form a crust or bridge when a container is emptied from below, leaving the top layer in place. Workers walking on the crust or bridge or working below the bridge on the floor of the container may be engulfed if the crust cracks or dislodges and a bridge collapses

    Other Hazards

    Uncontrolled introduction of substances

    The uncontrolled introduction of substances such as steam, water or other liquids, gases or solids may result in drowning, immersion, being overcome by fumes (for example vision and odour impairment from hydrogen sulphide (H2S), inability to breathe due to fine grain or ceramic dust), or other harm depending on the nature of the substance.

    Combustible engines, vehicles and liquid petroleum gas (LPG) forklifts operating close to the opening of the confined space can cause a build-up of exhaust gases, including carbon monoxide, in the space.

    Biological hazards

    Contact with micro-organisms, such as viruses, bacteria or fungi, may result in infectious diseases, dermatitis or lung conditions such as hypersensitivity pneumonitis. Sewers, grain silos and manure pits are examples of confined spaces where biological hazards may be present.

    Mechanical hazards

    Exposure to mechanical hazards associated with plant may result in entanglement, crushing, cutting, piercing or shearing of parts of a person’s body. Sources of mechanical hazards include plant such as augers, agitators, blenders, mixers and stirrers.

    Electrical hazards

    Electrical hazards may cause electrocution, shocks or burns, and can arise from cables, transformers, capacitors, relays, exposed terminals and wet surfaces where electrical circuits and electrically powered plant are used.

    Further guidance is available in the Code of Practice: Managing electrical risks in the workplace.

    Skin contact with hazardous substances

    The nature of a confined space could give rise to an increased likelihood of skin contact with surface contaminants. Skin contact with hazardous substances may result in immediate health effects such as burns, irritation or allergic dermatitis, or longer-term systemic effects.

    Noise

    Noise generated in a confined space from the use of plant, the work method or process may be amplified due to reflections off hard surfaces. Exposure to hazardous noise may result in hearing loss, tinnitus and other non-auditory health effects. Hazardous noise may also prevent workers from hearing warning signals and distract workers from their work.

    Further guidance is available in the Code of Practice: Managing noise and preventing hearing loss at work.

    Manual tasks

    Hazards arising from manual tasks may be exacerbated by physical constraints associated with working in a confined space. Additional hazards may arise from the use of personal protective equipment (PPE) that restricts movement, grip and mobility.

    Further guidance is available in the Code of Practice: Hazardous manual tasks. Radiation

    The health effects associated with radiation depend on the type of radiation involved. Sources of radiation include radioactive sources, X-rays, lasers, welding flash, radio frequency and microwaves.

    Environmental hazards

    Environmental hazards associated with work in a confined space may cause or contribute to harm. Examples of environmental hazards include:

    • heat or cold stress arising from the work, process or conditions;

    • slips, trips and falls arising from slippery surfaces or obstacles; and,

    • inadequate lighting.

    Further guidance is available in the Code of Practice: Managing the work environment and facilities.

    Hazards outside the confined space

    Where the confined space has a vertical opening, there is a risk that people could fall in.

    Traffic hazards are a concern where confined space entrances or exits are located on footpaths or roads. There is the potential for workers entering or exiting the space to be struck and injured by vehicle traffic.

    Work done outside the space, but near openings to it, can contaminate the atmosphere inside the space. A common example is the exhaust gases from an internal combustion engine. There may also be potential for fire or explosion where hot work is done in areas next to confined spaces that contain flammable atmospheres.

    Additional physiological and psychological demands

    Working in a confined space may impose additional physiological and psychological demands over and above those encountered in a normal working environment.

    Consideration should be given to a worker’s:

    • physical ability;
    • ability to work in a restrictive space (for example claustrophobia); and,
    • ability to wear the PPE required to do the work (for example respirators).
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    The WAHA would like to acknowledge the above information and guidance has been provided by the Safe Work Australia Model Code of Practice: Confined Spaces.