Hazardous locations command the use of explosion proof fixtures to prevent accidental combustion of flammable substances in the environment. Understanding the ratings that dictate their applications is a salient step in setting up industrial lighting systems. Skipping this step could result in devastating accidents on the site, as well as an increase in spending when purchasing the lights (equipment with higher levels of explosion proof protection are usually more expensive).
In order to ensure accuracy when buying explosion proof lights, it is advisable to focus on both general classifications (Class I, II, III) and classified groupings (A, B, C, D, E, F, G). The latter singles out specific flammable materials that could be present in the applicable hazardous location. Previously, we covered Class I, Groups A and B (acetylene and hydrogen); as well as Class I, Groups C and D (ethylene and propane). For the last installment in the classified groupings series, this article will expound on Class II, Groups E, F and G.
Group E (Metal Dusts)
Group E flammable materials include aluminum and magnesium. Aluminum is a sturdy metal with anti-corrosion properties (via passivation). In solid metal form, it is very difficult to ignite, as to melt the material, one would have to reach 1,220.58 °F. Problems with aluminum arises when it is in dust or powder form. As a dust cloud, workers could burn the substance with welding tools, torches, electrical equipment and static charges. Magnesium, in dust form, is also volatile for the same reasons. In fact, both materials (aluminum and magnesium) are often combined to create a strong alloy. In addition to being highly flammable and electrically conductive, metallic dusts in Group E are abrasive. This means that they can cause machines and tools to overheat, should the materials come in contact with motor bearings. Because they are electrically conductive, the substances can also cause premature failure of electrical equipment.
The presence of solid, non-dust form of aluminum and magnesium (e.g., aluminum casings on fixtures) does not call for explosion proof protection from Class II, Group E. If this were the case, then almost all residential homes and commercial buildings would need explosion proof equipment! It is when these materials are in dust or powder form that they become hazardous.
Group F (Coal Dust)
Group F flammable substances are carbonaceous dusts, i.e., mostly coal dust. Compared to Group E materials, this grouping comes with lower ignition temperatures, higher thermal insulating properties and are semi-conductive in nature. Other substances in this category includes carbon black, charcoal dust and petroleum (coke) dust. Such Group F substances are typically found in oil refineries, petrol processing plants and mining operations. Fortunately, these materials are not commonly found in establishments outside of their intended applications.
Group G (Flour, Plastics and Chemical Dusts)
Volatile materials in Group G are more complex than substances in Groups E and F. These compounds are not electrically conductive, but they do have exceptionally high thermal insulating properties. As a result, Class II, Group G explosion proof equipment usually have low surface temperatures to prevent accidental ignition. Facilities that need this level of protection are the following: flour storage buildings/processing plants, grain silos, chemical processing/storage buildings and plastic manufacturing establishments. Not a lot of people are aware that flour and other starches are flammable. The material is made up of sugar molecules, which can burn easily. The main issue with such substances is their fine characteristics when suspended in the air (in dust cloud form). One to two grams of dust per cubic foot of air is enough to trigger unwanted ignitions; hence, active ventilation is a must to prevent concentrated formations.
To conclude, if the applicable facility does not use, work with, handle or work around the flammable substances mentioned above, then there is no need for explosion proof protection for that specific material. For thoroughness and peace of mind, it would be best to engage in atmospheric testing to remove any doubt that one may have about volatile contents present in the hazardous location.