Compliance with flammability requirements for ammonia refrigeration systems.

Ammonia has been used as a refrigerant for over 150 years. It is flammable and therefore requires careful safety consideration in the design and operation of refrigeration systems, but ignition of ammonia is a very rare occurrence and is virtually unknown in systems which comply with European Standards requirements. This paper provides an overview of the legal framework to this topic, including the requirements of regulations derived from the ATEX directive 94/9/EC (in the UK this is the Dangerous Substances and Explosive Atmosphere Regulations (2002), known as DSEAR). The paper explains the procedure to be followed in conducting a hazard analysis for a new installation and highlights some difficulties with EN60079, the standard used for risk assessment of hazardous areas. A new approach, using software to model potential releases and calculate the zoning requirements, is described. Details of the basis of the software are given, and the effect on the compliance requirements of adopting this new approach. The paper concludes with some practical examples of zoning for various types of ammonia plant.