Risk assessment for natural refrigerants

Industrial and food refrigeration, domestic refrigerators, climate control and air conditioning... all these applications are part of our daily lives. Producing cold has become essential and self-evident in our modern society, both from the point of view of food safety (preserving stocks and maintaining their sanitary, organoleptic and nutritional qualities) and human well-being (air conditioning and environment treatment).

In the vast majority of applications, the refrigeration systems currently in use are based on vapour compression cycles and phase change of a refrigerant. Until now, refrigerants from the halogenated hydrocarbon family (CFC, HCFC) have been widely used, mainly because of their safety (non-toxic and non-flammable) and good thermodynamic performance. At the same time, other so-called "natural" fluids, more delicate to handle but more efficient from a strictly thermodynamic point of view, are also used on industrial sites: these include ammonia (widely used in the food industry) and hydrocarbons (used in the chemical and petrochemical industries).

In recent years, because of their impact on the environment (destruction of the ozone layer and the greenhouse effect), the use of halogenated refrigerants has been progressively restricted. In this context, the use of "natural" refrigerants is becoming a possible solution.

However, the technological risks associated with these fluids - flammability, explosivity and toxicity - mean that this solution must be approached with caution. In order to assess the appropriateness of using these fluids, it is essential to evaluate the risks associated with them. The methods to be used depend on the quantity of fluid involved.

At the industrial scale, where major risks are to be feared, a certain amount of experience and numerous studies have enabled us to establish a rigorous approach. The first part of this article describes this approach. It falls within the scope of environmental protection legislation governing classified installations.

The second part of the article deals with the risks associated with the use of "natural" refrigerants on the typical scale of refrigeration plants:

• in the case of hydrocarbons, where large fluid loads are rarely encountered (from a few tens of grams in the case of domestic appliances, to a few kilograms for commercial applications), the application of methods developed for industrial installations is not recommended (lack of experimental data, models and scenarios not validated at this scale). In this case, methods are proposed to enable an approximate assessment of the orders of magnitude of the risk associated with these small installations;

...