In the past 5 years of the currently available HSE statistics 27 people have died in the UK from asphyxiation or drowning at work. However, in just the last few months there have been 2 incidents of asphyxiation deaths due to refrigeration leaks. The first in August 2018 killing a trawlerman and hospitalising 3 more and the second in October 2018 suspected of killing two contractors at a poultry factory.
The risks of refrigerant gas leaks are two fold asphyxiation from a depletion of Oxygen and toxic exposure to gas which is immediately dangerous to life and health. According to the Workplace Safety and Health Institute on behalf of the World Health Organisation and International Labour Organisation it is estimated worldwide deaths from hazardous substances at work are at an all-time high at 651,279 deaths per year and rising based on the most recent applicable statistics.
In the case of the trawlermen according to the Marine Accident Investigation Branch (MAIB) it is believed the R22 gas entered the tank via an evaporator tube failure. No safety procedures for entering the tank had been completed prior to entry. As R22 is heavier than air it settled at the bottom of the tank when the Trawlerman entered the area the Oxygen level was so low he lost consciousness he was later found by 3 other crew member who were later hospitalised after becoming dizzy, confused and suffering a shortness of breath. The Oxygen levels were later tested by the MAIB and found to be at less than 6%.
The second case at the poultry factory involved two sub-contractors who died at the scene, this is still under investigation but initial findings suggest a leak of refrigerant gas.
Oxygen concentration levels are as standard found at 20.9% below 18% continuous ventilation is required, between 12%-16% people will suffer nausea lack of concentration and headaches, below 10% loss of consciousness and 6% or less a cessation of breathing and death within a few minutes.
As most refrigerant gasses are heavier than air it is possible to have safe levels of Oxygen at the entry point of a confined space only for oxygen levels to be dangerously low in lower areas. For this reason it is sensible to pre-entry test gas levels and continuously monitor as any maintenance work is performed in case of a change in conditions.
As with any confined space risk assessment is vital and risk should be kept as low as reasonably possible with options for escape included as part of this and monitoring of conditions playing a vital part.
Walk in refrigeration units also pose significant risks as they can be left unattended for significant periods and if storing potentially hazardous substances the only method of protecting people on entry is to monitor continuously within the refrigeration unit. I was personally involved in a case in Kent after employees lost consciousness when entering a large walk in refrigerator storing among other things Liquid Nitrogen tanks. When one of the tanks leaked overnight it depleted the Oxygen to the point when an employee opened the door to enter they immediately lost consciousness. Fortunately, on this occasion no one died but this common occurrence is easily preventable with fixed gas detection and low cost personal monitors in conjunction with risk assessment and management plans.