Document ID: chunk:federal_register_of_legislation:F2016L00405:body:0:p9
Version: federal_register_of_legislation:F2016L00405
Segment Type: other
Provision Reference: 
Character Range: 20390–24819

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                                                                                                                      Examples
Substance stored in the confined space or its by-product(s)                                                                     * build-up of hydrogen sulphide in sewers and pits
                                                                                                                                * release of toxic substances e.g. hydrogen sulphide in tanks
                                                                                                                                  of decomposing organic material, especially when the material is disturbed
Work performed in the confined space                                                                                            * use of paints, adhesives, solvents or cleaning solutions
                                                                                                                                * welding or brazing with metals capable of producing toxic fumes
                                                                                                                                * exhaust fumes 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 gas or vapour
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 level
Air normally contains 21% oxygen by volume, although oxygen levels of 19.5% — 23.5% 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, for example, 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 fumes
    * depleted inside metal tanks and vessels through surface oxidation (for example, when rust forms)
    * consumed during combustion of flammable substances
    * 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
    * there is a leak of oxygen from an oxygen tank or fitting while using oxy-acetylene equipment.

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