Site visits provide direct insight into the grain industry’s educational needs. During a recent audit of bin-entry permits at a grain facility, I asked the manager about portable electrical equipment used in bins and his knowledge of electrical classifications for combustible dust. He admitted he was unfamiliar with these standards, so I briefly explained Class II hazardous locations and proper equipment identification. Realizing that others lack this knowledge as well, I decided to write this article.
It is important for industry personnel to understand hazardous electrical locations. These locations include areas where fire or explosion potential exists because of the presence of flammable gases, vapors, liquids, combustible dusts or ignitable fibers, and where electrical equipment could ignite them through sparks, arcs or hot surfaces. These locations are found in grain handling, biofuel and processing facilities. This article will focus on Class II, Group G hazardous locations that pertain to combustible grain and flour dust.
Understanding Class II Hazardous Locations
Class II hazardous locations are categorized into Division 1 and Division 2 for clarity and regulatory purposes. According to the Occupational Safety and Health Administration (OSHA), a Class II, Division 1 area is one in which combustible dust may be suspended in the air under normal operating conditions in quantities sufficient to produce explosive or ignitable mixtures, or where mechanical failure or abnormal operation of machinery or equipment might cause explosive or ignitable mixtures to be produced. These locations might also provide a source of ignition through the simultaneous failure of electrical equipment.
Consider the gallery floor of a grain elevator with open conveyance. This area may have combustible dust suspended under normal operating conditions in quantities sufficient to produce a combustible dust explosion.
A Class II, Division 2 hazardous location is one in which combustible dust will not normally be suspended in the air in quantities sufficient to produce explosive or ignitable mixtures, and dust accumulations will normally be insufficient to interfere with the normal operation of electrical equipment. However, combustible dust may be suspended in the air because of infrequent malfunctioning of handling or processing equipment, resulting in combustible dust accumulations on or near electrical equipment. These accumulations may be sufficient to interfere with the safe dissipation of heat from electrical equipment or may be ignited by abnormal operation or electrical equipment failure.
Electrical Protection Methods for Combustible Dust
Electrical equipment is considered safe for Class II, Division 1 and Division 2 locations if it utilizes protection techniques such as dust-ignition-proof construction or intrinsic safety. Dust-ignition-proof equipment is designed to prevent combustible dust from entering an electrical enclosure and to ensure that any heat, arcs or sparks generated inside the equipment cannot ignite dust accumulations or atmospheric dust suspensions outside the equipment. This often requires threaded conduit and dust-tight seals.
Intrinsically safe (IS) equipment is a design technique used in hazardous locations that prevents explosions by ensuring the device is incapable of releasing enough energy to ignite the surrounding atmosphere. Equipment designed and approved for Class II, Division 1 locations is also safe for Division 2 locations.
In addition to these protection techniques, Class II, Division 2 locations may use dust-tight enclosures to prevent dust from entering and accumulating inside the equipment, as well as pressurization, which uses clean, pressurized air to keep hazardous dust out of the enclosure or area.
Verifying Equipment Certification
To determine whether equipment is certified for Class II, Division 1 or Division 2 environments, examine the nameplate for markings confirming certification by a recognized testing laboratory, such as UL, CSA or FM. The nameplate should clearly specify the applicable class, group and associated temperature code, which demonstrate the equipment’s suitability for use in combustible dust atmospheres. This information is available on both fixed and portable equipment.
Employees in the grain industry need to understand not only the hazards of combustible dust but also the types of electrical equipment that can be used in hazardous locations.
The first step is ensuring that a qualified electrical engineer, following OSHA and National Electrical Code guidelines, has properly classified the applicable locations within the facility.
The second step is ensuring that electrical installations and equipment, both portable and fixed, meet the requirements. Remember, safety doesn’t have to be difficult. Simple steps, such as understanding Class II electrical locations, can prevent dust explosions and save lives.
Joe Mlynek is president and safety and loss control consultant for Progressive Safety Services LLC, Gates Mills, OH; 216-403-9669; and subject matter expert for Safety Made Simple, LLC, Olathe, KS.