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Intrinsic Safety

What does "intrinsically safe" mean?

You may have come across the term "intrinsic safety" or seen the reference that a piece of equipment is "intrinsically safe." Intrinsic safety is a requirement that may be applicable to devices that are being operated in areas with flammable gases or fuels. It means that the device is incapable of igniting those gases. In short, an intriniscally safe piece of equipment won't ignite flammable gases. ISA-RP12-6 defines intrinsically safe equipment as "equipment and wiring which is incapable of releasing sufficient electrical or thermal energy under normal or abnormal conditions to cause ignition of a specific hazardous atmospheric mixture in its most easily ignited concentration."

Many ultra ruggedized mobile computers will include intrinsically safe (I-Safe) specifications or approval ratings. Understanding I-Safe approval ratings can be a difficult proposition for even the most informed customer. Intrinsically safe areas are hazardous environments where flammable gases, vapors and liquids are stored and manufactured. These areas are prevalent in many of today's manufacturing facilities including chemical plants, paint manufacturers, oil refineries, textile mills, etc.

Each designated hazardous environment has specific certification requirements for all equipment used in the I-Safe area. Intrinsically safe equipment must carry a label, which specifies the exact I-Safe rating for the equipment and the name of the NRTL (Nationally Recognized Testing Laboratory) who tested it. Testing laboratories have very stringent certification requirements that vary according to the level of I-Safe approval desired. Therefore, each intrinsically safe device is certified for different levels of I-Safe approval, and can only be used in specific hazardous environments. The bottom line is that close attention must be given to the specific I-Safe approval certification for each individual piece of equipment. Just because a device has an I-Safe rating, does not mean that the device can be used in any I-Safe area.

I-Safe approval certifications are made up of multiple classes, groups and divisions that correspond to the specific hazardous environment a device is approved to operate in. Each class consists of two divisions and certain classes have multiple groups. For example, Class I includes flammable gases, Class II includes flammable dust, and Class III includes flammable fibers. Each class has two divisions. Division 1 includes environments where explosive material is present in the air at all times. Division 2 includes environments where explosive material is stored in sealed containers, and explosive material is only present for short time intervals (when a failure occurs or during maintenance). Also, Classes I and II are broken down into groups that correspond to the explosive properties of each specific material. For example, Group A includes Acetylene and Group E includes aluminum dust. In addition, I-Safe approval ratings differ significantly from country to country. A device that is I-Safe certified for use in the U.S. may not be certified in Europe. Needless to say, understanding the differences between I-Safe approval certifications can be a full time job, and can make the purchasing decision for an I-Safe device a very difficult and lengthy process. However, to ensure the safety of your facility and personnel this verification process is extremely important, and cannot be overlooked. In order to create a "gold standard" for I-Safe products, in June 2003, I-Safe equipment will require ATEX certification. This certification standardizes I-Safe approval ratings and will be used in the U.S. and Europe. This should help make understanding I-Safe approval ratings much easier.

(from "Can your rugged machine really handle the job?" by Tim Crews, published in Pen Computing Magazine issue #52)