2.2.1 Hazards of fuels other than hydrogen

Many fuel cells use hydrogen produced by the reforming of hydrocarbon fuels; other high temperature fuel cells are able to utilise suitable hydrocarbons directly. The processing and/or use of these hydrocarbon fuels will produce carbon dioxide. Appropriate measures, such as containment and ventilation, should be taken to ensure that any carbon dioxide effluent stream is effectively discharged and does not produce an asphyxiation risk [2].

Natural gas (methane) is lighter than air and will tend to diffuse upwards, but at a much slower rate than hydrogen. The explosion limits for natural gas (5-15% v/v) are also much narrower than hydrogen [3]. The characteristics of both fuels should be considered for any dual fuel systems. The pipe work and equipment used to supply natural gas should also be suitable and designed to an appropriate standard [4].

Liquefied petroleum gas (LPG) is considerably heavier than air, especially when cold, for example when taken directly from a liquid storage vessel. In the event of a leak, LPG vapour will usually percolate downwards and may accumulate on the floor or in low-lying sumps, rapidly producing a flammable atmosphere. Mixtures containing 2-10% v/v LPG in air will readily ignite and explode [5]. The significant differences in the buoyancy and dispersion characteristics of the two fuels should be carefully considered in systems where LPG and hydrogen may both be present. The pipe work and equipment used to store and supply LPG fuel should also be suitable and be designed to an appropriate standard [4].

Methanol can be used directly by some types of fuel cell. This fuel has some hazards that demand particular attention. In addition to being a highly flammable liquid, methanol is also toxic by inhalation, ingestion and notably, by skin absorption [6]. Appropriate precautions such as containment and ventilation should be taken to prevent spillages and the accumulation of hazardous methanol/air mixtures whenever it is used.

Compared to the hazards associated with more conventional equivalents to fuel cells e.g. natural gas boilers and batteries, some different hazards have to be taken into account, including not only the fuel cell but also the means of fuel production, storage and transportation. Regulations applicable to natural gas systems are detailed in Appendix A1