The switch over to low pressure of a compressor helped to detect 2 successive ammonia (NH3) leaks in the refrigeration installation of a brewery/lemonade plant using 840 kg of NH3. This installation had 2 plate heat exchangers for cooling glycol water through heat exchange with NH3. A 1st NH3 leak in the glycol water circuit occurred on 25/11/06 on one of the heat exchangers and the 2nd leak occurred on 16/01/07 on the second heat exchanger.

The 2 incidents were no doubt caused by corrosion of the circuits or a thermal shock with deformation of the heat exchanger cartridges. As the pressure in the NH3 circuit was greater than that in the glycol water circuit, a proportion of the NH3 contaminated the glycol water circuit. According to the operator, not adapting the compressors to the refrigeration installation would have caused the heat exchangers to freeze.

The operator called an external company (the installation’s supplier) on 5 to 9 March 2007 to analyse the causes and consequences of these 2 incidents and take the first measures. To degas the NH3 from the glycol water, after 12/03/07 the operator placed the mixture in the open air in an expansion tank located above the machine room, but outside of the building. The operator therefore assessed the amount of NH3 part in the glycol water, then released into the atmosphere during venting of the glycol water circuit, to be 480 kg (240 kg through leakage).

The enquiry carried out seemed to indicate that the automated systems and control parameters of the refrigeration installation had not been totally controlled. Certain items of equipment and in particular the heat exchangers were no doubt already fairly corroded. The safety report carried out on the installations did not take this type of scenario into account. Several assessments carried out at the operator’s request, in particular, enabled the automated systems used in the refrigeration installation to be adjusted.