Confined Spaces Risks
In the U.K. the Confined Space Regulations 1997 (S.I. 1713) require employers to assess the risks associated with asphyxiation, explosion, fire, toxic substances etc. in any space which presents such hazards. Safe systems of work and rescue plans must be provided. Additionally under the Management of Health and Safety at Work Regulations 1999 (S.I. 3242) employers are required to assess the risks of all the processes and tasks undertaken in the enterprise. Practices and training must be aligned to the results of these assessments so as to minimise risks. Working with industrial gases may affect the balance of the gases that make up the atmosphere in the working environment. Many processes like welding and cutting not only consume oxygen from the air around but may also create gaseous contaminants that may affect the atmosphere in the working area. Ultra violet light from electric arc welding may also affect the oxygen in the atmosphere in close proximity to the weld.
One of the biggest risks is ashyxiation caused by the reduction of the oxygen in the atmosphere when gases leak into the working environment. All joints in all systems used to carry gases to their point of use should be leak free and should therefore be frequently tested with an approved leak test solution. It should be noted here that when working with cryogenic liquids like nitrogen the expansion of liquid gas into its vapour state may create additional risk of asphyxiation. One litre of liquid nitrogen will expand into 683 litres of nitrogen gas which does not support life. Attention must be given to vessels storing gases in their liquid form since open vessels will leak gas into the environment all the time and pressurised vessels are fitted with relief valves and burst discs which may allow gas into the working area. There are special guidance notes on the storage of cryogenic gases within buildings. The British Compressed Gases Association has also published a Code of Practice (number CP30) which gives guidance on the safe use of liquid nitrogen dewars. There are special guidance notes for the entry into confined spaces where it is suspected that the atmosphere is dangerous. Breathing apparatus will be required and the user must know how to operate it. Help should be summoned immediately and control kept of the situation, noting the time of entry into the suspect area of anyone involved with a rescue and the condition and contents of their breathing apparatus. Please refer to "Controlling the risks of inert gases" click here The use of fuel gases like acetylene, propane and hydrogen may create the risk of explosion. Leaks of fuel gases into the working environment would allow the creation of flammable or explosive mixtures in air. The flammability range of every fuel gas is different . Some gases have a very low lower limit which means that in a working environment which is not well ventilated an explosive mix can be created very quickly. Additionally the energy required to ignite some flammable mixtures is very low thus increasing the risk further. Fuel gases are also asphyxiants so leaks will reduce the breathable oxygen in the vicinity. It is important to know whether gases are heavier or lighter than air and thereby to understand where leaks will accumulate. The risk of fire in the work area is significantly enhanced when there is more than the normal amount of oxygen in the environment. This circumstance will arise if an oxygen system is leaking into the work area. Materials that do not burn in air may burn in an oxygen enriched atmosphere. The amount of energy needed to ignite a material in an oxygen enriched atmosphere is also reduced. Great care must be taken if individuals are exposed to an oxygen enriched atmosphere; clothing and hair will absorb the oxygen. If you suspect that this has happened the person should get into the fresh air as soon as possible and remain there for at least 15 minutes to normalise their situation. The source of the leak has to be traced and sealed off. The risks detailed above may be minimised by the correct management of the working atmosphere. Ventilation is key and in some situations forced ventilation may be required to ensure that the working atmosphere remains normal in terms of the breathable oxygen and contaminants like carbon dioxide and carbon monoxide (which are often present as the products of combustion) are removed to a safe place. Gas monitors are available to indicate the level of oxygen in an area and other gas specific detectors are also available to assist in the indication of enhanced risk. Monitors may indicate a problem but they will not solve the issue. Full risk assessments are vital taking note of the fact that operators may be adversely affected by the onset of abnormal atmospheres and may be unable to judge situations and react at normal speed. Entry into confined spaces must be covered by a safe system of work (e.g. Permit to Work scheme) based on
The system should address the following points:
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