Gases in enclosed spaces
13 February 2018
The British Compressed Gases Association (BCGA) has recently published guidance that can be used in the assessment of risk associated with gases in enclosed workplaces, to identify where hazardous atmospheres may occur and the appropriate control measures.
Ambient air is primarily composed of two gases, nitrogen at approximately 78% and oxygen at 20.9%. Changes to the air composition can result in a potentially hazardous atmosphere. Human senses cannot detect different compositions in the atmosphere and are not a valid indicator.
Changes to the composition of the air will occur from the release of gas(es) into the local environment. Examples include evaporation, leakage and process exhaust. There is also the potential for gases to enter the workplace from external sources. Examples include the release of gases from neighbour sites, or concentrations of naturally occurring gases. The changes will be more pronounced in an enclosed space and where there is inadequate ventilation.
It should also be borne in mind that even before the introduction of stored gases into certain workplace situations, gases and low oxygen concentrations may have been generated within an enclosed space by natural decay mechanisms such as the production of hydrogen sulphide from stagnant water, or the corrosion (oxidation) of some metals which can deplete the available oxygen. Atmospheric checking prior to entry to an enclosed space is therefore vital.
Incidents can occur unexpectedly, and may be serious, and sometimes fatal. The BCGA has stressed that all personnel accessing an enclosed workplace should be aware of the hazard(s) associated with non-respirable atmospheres and be given the necessary equipment, information, instruction and training.