It only takes a spark to start a fire or cause an explosion, especially when flammable gases or vapours are present under the right conditions. There are industries that operate in these types of hazardous environments where the potential for explosions is extremely high, such as chemical plants, oil refineries, paint shops, cleaning facilities, tanks and loading facilities for flammable gases, liquids and solids. OSHA defines hazardous locations as:
Areas where flammable liquids, gases or vapors or combustible dusts exist in sufficient quantities to produce an explosion or fire. In hazardous locations, specially designed equipment and special installation techniques must be used to protect against the explosive and flammable potential of these substances.
Two types of specially designed equipment for use in hazardous locations are explosion proof and intrinsically safe.
Explosion proof is a protection technology that guarantees the housing or enclosure has been designed and constructed in such a way that it is capable of containing, controlling and venting any possible flash or explosion. Enclosures of this kind are typically made of stainless steel or cast Aluminum and are of an appropriate mass and strength that they will safely contain an explosion if flammable gases or vapours should penetrate the housing and the internal electrical components or wiring should cause an ignition. The amount of power to or from the device is not of concern.
Intrinsically safe is an explosion protection technique that ensures that the electrical circuit and its wiring is engineered in such a way that it is not capable of releasing enough energy, or producing a high enough temperature under any condition and thus is not able to cause an ignition of itself or the surrounding area. This specifically designed equipment does not require a special enclosure or housing. Instead, the amount of power the device has is typically controlled through the use of intrinsic safety barriers and as a result, this type of equipment can be used only for very low power applications.
Gas detectors for hazardous location applications must meet strict codes and standards and can be built as either explosion proof or intrinsically safe. Intrinsically safe gas detectors are very common in Europe and explosion proof is the more commonly used method in North America for fixed gas detection systems. With the rugged housing to withstand harsh environments and no limits on the types of sensors, the explosion proof gas detector can be used in a wider range of applications and in particular, for applications that require high power.
|Explosion Proof Gas Detector||Intrinsically Safe Gas Detector|
Contains and controls the explosion, does not prevent an internal explosion
|Prevents an explosion, does not contain an explosion|
Stainless steel or cast Aluminum
Large, heavy, often bulky
Power is not controlled, operates at normal power levels
|Power is controlled, operates on low power levels|
|Installation||Difficult: heavy, bulky, requires heavy conduit and seals||
Easy: small and does not require expensive accessories
|Maintenance & Calibration||Non-intrusive calibration may be done without disconnecting power. Power must be disconnected if opening the device.||
Non-intrusive calibration may be done without disconnecting power. Power must be disconnected if opening the device.
|Types of Sensors||Electrochemical, infrared, combustible /catalytic or PIDs||
Electrochemical (low current sensors only)
Oil Refineries, Drilling rigs on oil fields, Municipal Treatment Plants, Chemical Storage Rooms, Loading facilities for flammable gases, liquids and solids
Allen-Bradley, Rockwell Automation (October 2001) Class/Division Hazardous Location. Retrieved from http://literature.rockwellautomation.com/idc/groups/literature/documents/wp/800-wp003_-en-p.pdf
Bob Svacina and Brad Larson, Turck Inc. (April 2000). Understanding Hazardous Area Sensing. Retrieved from http://www.parrinst.com/wp-content/uploads/downloads/2011/06/Svacina-Larson_Understanding-Hazardous-Area-Sensing_Intrinsic-Safety.pdf
CorDEX Instruments Ltd. (2010). Intrinsically Safe or Explosion Proof? Understanding the technology. Retrieved from http://www.transcat.com/media/pdf/cordex-is-explosion-proof.pdf
RKI Instruments, Inc. (February 19, 2008). What’s the Difference Between “Explosion Proof” & “Intrinsically Safe”. Retrieved from http://www.rkiinstruments.com/pdf/FAQ_Explosion_Proof.pdf