Incidents relating to thermal fluid systems are unfortunately more common than we might realise, and can be extremely serious. The fire and explosion hazards with thermal fluid systems have been re-emphasised by recent incidents. These incidents have a direct bearing on the estimated 4,000 UK companies that operate thermal fluid systems. Water or steam can be used as heat transfer fluids, but when high temperatures are needed organic fluids, which are capable of forming explosive atmospheres, are often used. Although fire and explosion hazards of low flash point flammable liquids are generally recognised, similar hazards with high flash point materials, such as thermal fluids, are often missed. These heat transfer fluids are often handled at temperatures above their flash point. The Health and Safety Executive recently issued a prohibition notice to a UK company following a major thermal fluid incident and significantly, following that incident, has identified thermal fluid systems as a fire and explosion hazard. There have been other serious incidents this year. Although not under HSE jurisdiction, there was a recent thermal fluid-related explosion and fire at a German panel products plant which tragically caused three fatalities. Most companies will be aware that any system that operates above the flash point of the thermal fluid falls under the "Dangerous Substances and Explosive Atmosphere" Regulations 2002 (DSEAR). However, many people are unaware that heat transfer fluids based on mineral oils degrade over time. This degradation can cause the fluid's flash point to decrease dramatically, so that thermal fluids which were not flammable at the operating temperature when they were initially installed may, over time, become flammable at the operating conditions. Also, high flash point materials (such as thermal fluids), can form explosive mist atmospheres when handled under pressure, even at temperatures below the flash point. The DSEAR regulations require that the risk from dangerous substances (flammable materials) is assessed and eliminated or reduced. Systems need to be put in place to reduce the risk and manage the residual risk. The ATEX directives require the hazardous areas to be identified. Regular thermal fluid testing and the results obtained will indicate the physical condition of the fluid and the degree of risk in the event of a fluid release. However, flash point testing alone is not enough to comply with DSEAR. Procedures are also needed to change out the thermal fluid, or remove the lower flash point components from the thermal fluid. Many companies operating thermal fluid systems may not be aware of this. This paper discusses recent incidents of fires and explosions which have occurred in thermal fluid systems, and makes practical recommendations for how such incidents can be avoided. These include carrying out Area Classification on thermal fluid systems, methods to avoid or limit mist formation, avoiding ignition sources and installing proprietary equipment which removes the lower flash point components from the thermal fluid.
