Explosion prevention-the broader picture

Over 100 years, the electrical engineering community has developed and refined a whole series of ways to create electrical equipment that can be used safely where flammable substances are present in the surroundings. The initial designs were intended to cope with gas atmospheres in mines. These were followed by designs for a wider range of applications in the expanding chemical and oil refining industries, while bringing up the rear were standards for use in dusty atmospheres, as found, for example, in flour milling, wood finishing and some chemical processes. Despite all this effort, we have not stopped fires and explosions from occurring, sometimes with quite localised effects, and sometimes with devastating consequences. It is clearly necessary to address not just the ignition risks from electrical equipment, but all the potential sources of ignition in a plant, and other approaches to making a site acceptably safe. The author discusses ignition sources, avoidance of explosive atmospheres, measuring vapour levels, mitigation measures, European Directives, nonelectrical equipment standards, and equipment reliability. The author concludes that with so many uncertainties in the equation, perhaps it is not wise to base safety on the single technique of avoiding ignition sources, unless the plant is extremely simple.