A hazard-based approach to designing with modern refrigerant gases for naval ships

The Montreal Protocol on substances that deplete the ozone layer and EU Regulation 517/2014 on fluorinated greenhouse gases limit the continued use of R134a and other commonly used refrigerants in domestic and industrial applications, including the marine sector. Many navies have also committed to comply with the legislation even though they are often exempted. The legislation is driving the use of alternative refrigerants that have higher flammability or toxicity characteristics than those previously used. The introduction of these alternative refrigerants potentially introduces new hazards that must be considered in systems design. This is especially pertinent in naval vessels which typically have large equipment cooling requirements compared to similar size commercial ships, furthermore the equipment is often located in densely-packed machinery spaces, and with a higher crew occupancy. Naval vessels also face additional operational risks and have a greater requirement to maintain capability in the event of an incident or accident.
Standards and guidance documents are available for designing with refrigerants of these alternative types, however these are not tailored to a naval application, and do not consider the context of the system and operational constraints, so may result in an increase in cost and weight to the ship design that is disproportional to the perceived risk. This paper reviews the current literature and standards to understand the properties of the refrigerants, the safety controls that can be employed and in what context they are used. The individual hazards associated with the different classes of refrigerant are identified and possible mitigations for each are investigated with reference to the naval context.
These findings are used to define a hazard-based approach to systemdesign. The method is compared to current standards to demonstrate the impact on the design. It is found that the hazard based approach results in different controls being incorporated in the design than would be used following the requirements from international standards or classification society rules. The proposed approach is recommended for consideration for future naval ship designs and included in classification society rules.