Intrinsic Safety vs. Explosion-Proof
These are different approaches to prevent a malfunction of electrical equipment from initiating an explosion through ignition of gases present in the surrounding atmosphere.
Intrinsically Safe devices, through proper electronic design, are not capable of causing an explosion because the energy levels are kept at a low enough level.
Explosion-Proof devices are designed so that if an explosion does occur inside the enclosure, it will be contained within the enclosure and not ignite surrounding gases. This containment is done through careful design of the enclosure so that the resulting explosion is not only contained; but the heat is also dissipated through the large surface of the flanges or threads of the enclosure. Consequently, if the integrity of the enclosure is compromised, (because of a scratch across the flange face, or incomplete tightening of the cover) there is a risk of an explosion. The net result is that Explosion Proof protection has a higher level of required maintenance than an Intrinsically Safe system..
For these reasons, Gizmo Engineering prefers the Intrinsically Safe approach.
Division, class and group
The hazardous location ratings are divided into Class, Division, and Group to indicate the existence of flammable gases or vapors, ignitable dust, fibers, or filings under normal or unlikely conditions of operation. The concept was developed for safe operation in hazardous areas, particularly around petro-chemicals, flammable gasses and dusts. Only a Nationally Recognized Testing Lab (NRTL) such as UL or CSA can approve I.S. products.
Class l Areas in which flammable gases or vapors may be present in sufficient quantities to be explosive or ignitable.
Class ll Areas made hazardous by the presence of combustible dust.
Class lll Areas in which there are easily ignitable fibers or flyings present, due to the type of material being handled, stored or processed-but in which such fibers or flyings are not likely to be in suspension in the air in quantities sufficient to produce ignitable mixtures.
Division 1 - Normal Situation: A hazard is present in the everyday normal production operation or during frequent repair and/or maintenance activity.
Division 2 - Abnormal Situation: Potentially hazardous material is expected to be safely confined within closed containers or closed systems, and will be present in the atmosphere only through accidental rupture, breakage, or abnormal operation.
Group A, B, C & D Gases and vapors in Class l locations are classified into four groups, by the code A, B, C, and D. These materials are grouped according to the ignition temperature of the substance, its explosion pressure and other flammability characteristics.
Groups E, F & G apply to Combustible dusts.
Intrinsic safety certification requires the production site is subject to regular audits to conform to a range of compliance measures. These facility audits on a regular basis ensure adequate inspection, testing and acceptance techniques are in use in the manufacturing process. During an audit, production records, product documentation, and product samples are audited to verify continued compliance. These efforts demonstrate that not only are the products in compliance, but manufactured repeatedly in compliance with approval standards.