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French Agency for Food, Environmental and Occupational Health & Safety

Hyperbaric occupational activities: new practices to improve safety require special regulations

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News of 15/10/2014

Workers who perform their activities under hyperbaric conditions (pressure higher than the ambient atmospheric pressure, i.e. > 100 hPa), may do so immersed in water (divers, scientists, military personnel, rescue teams, etc.) or without immersion (medical staff, tunnel diggers, etc.). They are exposed to the risks inherent to their occupation, in addition to specific risks linked to hyperbaric environments. In France, while there are regulations defining work methods and the gaseous breathing mixtures authorised according to the work sector, they do not have any special provisions concerning gas-recycling breathing apparatuses (rebreathers) or professional free-diving activities. To ensure the drafting of a regulatory framework suitable to all these practices, the General Directorate for Labour formally requested ANSES to conduct an expert assessment on the health effects of occupational exposure to breathing gas mixtures other than air in hyperbaric contexts. A specific focus has been provided with regard to the use of rebreathers and the risks of free-diving. In the opinion and report relative to this request, ANSES concludes that gaseous mixtures, rebreathers and free-diving offer a new outlook and opportunities in terms of safety and health in the hyperbaric occupational sector. Nonetheless, it wishes to stress the fact that the implementation of these practices requires adherence to special recommendations for each type of activity.


A hyperbaric environment is defined in the regulations as an environment in which workers are required to perform under relative pressures that are higher than the ambient atmospheric pressure (> 100 hPa). These workers perform activities either under water (divers, scientists, military personnel, rescue teams, etc.), or without immersion (medical staff, tunnel diggers, etc.).


The total number of workers exposed to hyperbaric conditions in France is estimated to be approximately 10 000 people, with highly diverse work sectors and working methods specific to each profession.


Exposure to hyperbaric environments can cause both acute and chronic disorders (barotrauma, intoxication from inhaled gases, decompression sickness, etc.) of variable severity (from simple ear discomfort to death). Symptoms may appear during or following time spent in an environment subjected to higher-than-atmospheric pressure.


ANSES's work: support for drafting regulations


Among other things, the current regulations define working methods (open-circuit self-contained diving gear, umbilical cables, chambers, etc.) and authorised breathing gas mixtures (air, pure oxygen, mixtures, etc.) for each work sector. However, the regulations do not provide any specific provisions on the use of rebreathers (self-contained apparatuses that captures exhaled gases to recycle them) or on free-diving. The regulatory situation on the international level is similar to that of France.


In order to extend the regulations to these new areas, ANSES was asked by the Directorate General for Labour to conduct an expert assessment of the health effects of occupational exposure to breathing gas mixtures other than air in hyperbaric contexts. The Agency has been asked specifically to:

  • identify and characterise the population groups involved in these activities;
  • define the short- and long-term health effects on the human body of use of the equipment and gaseous mixtures identified, with a focus on the use of gas-recycling breathing apparatuses (rebreathers);
  • assess the risks of free-diving in an occupational context and potentially to issue recommendations for a suitable regulatory framework for this practice.

Risks specific to each work method, and a need for strict regulations and specific safety requirements


Air is the most common breathing gas mixture used for working in a hyperbaric setting, although its use is limited on the physiological level due to the toxicity of breathing gases, and in particular that of nitrogen (nitrogen narcosis). The use of breathing gas mixtures other than air during hyperbaric activities, either with or without the use of rebreathers, makes it possible to overcome some of these physiological constraints and thus offers new opportunities for the future of work activities in hyperbaric environments.


ANSES emphasises in its opinion and report that the use of breathing mixtures other than air, rebreathers and occupational free-diving activities provide certain advantages in terms of safety and health, as well as certain risks for workers that require the implementation of a suitable regulatory framework. Thus, after having described the profiles of the workers in question and the practices implemented in each work sector, the Agency has issued a series of recommendations for each of the work methods which aims to improve the safety and comfort of workers in hyperbaric settings.


ANSES recommends in particular that workers use breathing mixtures other than air for all activities performed at over 6 bars of absolute pressure (a depth of 50 meters) in order to minimise the risk of nitrogin narcosis. The Agency also recommends the use of rebreathers in certain contexts, including work requiring autonomous breathing, optimised decompression or as a backup method for work under high absolute pressure (at great depths).


However, implementation of these practices in an occupational context requires strict regulation and specific measures regarding work procedures, the choice of mixtures depending on the conditions of use (pressure, physical effort, etc.), the occupational training received, the qualification of equipment and apparatuses, the gas supply, and the availability of decompression equipment validated for occupational use.


Lastly, due to the particular risks of free-diving, ANSES strongly recommends that the regulations present the procedures for occupational free-diving separately from those for the other types of activities. It might also be appropriate to provide a special reference to occupational free-diving, including specific techniques and a specific training programme.