In North American, potentially explosive environments are classified into Divisions, Classes, and Groups. The Division indicates the likelihood that a substance will be present. The Class and Group indicate the nature of the substance.
Division 1 indicates the hazard is constantly be present. Division 2 indicates that the hazard is only rarely present. All portable wireless devices used in Division 1 locations must be rated intrinsically safe, or I-safe. I-safe products are suitable for use in Division 2 locations with one caveat.
| "For most devices, the jump from 'ordinary' to N-I is minimal in terms of price and performance. But the jump in price and performance from N-I to I-Safe is substantial." |
"The NEC allows Division 1-rated equipment to be used in Division 2 locations of the same Class and Group rating," says Patrick Helton, the senior product safety engineer with Intermec Technologies (http://www. intermec.com). But, explains Helton, a device only rated for use in Division 2, Class II,Group G and F locations may not be suitable for use in Division 2, Class I Group A, B, C or D locations.
Products rated non-incendive or N-I are suitable for use in Division 2 locations. Products rated N-I are not suitable for use in Division 1 locations.
I-safe and N-I portable devices produce electrical energy at a level below the threshold needed to ignite a potentially explosive environment. The other factor that must be considered is the maximum operating surface temperature of the portable device. Each portable wireless device used in a hazardous area must have a temperature rating equal to or lower than the area temperature rating.
"Besides using correctly certified tools for hazardous areas, there is the problem of carry through," says Jim Shields, a senior product specialist with Fluke (www.fluke.com). "Any time a worker passes through an area, any device in their possession needs to have the correct ratings. If not, accidental activation could have catastrophic results," adds Shields.
Other areas of concern are cables, connectors, and batteries. "External peripherals may not be able to be connected or disconnected from the device in the field," says Chuck Dourlet, the vice president of product marketing for Symbol Technologies' mobile computing division (www.symbol.com). "Also, batteries cannot be changed in many hazardous areas," comments Dourlet.
Manufacturers are responding to needs for I-safe and N-I products, but at a price. "Devices rated for use in hazardous locations cost more to produce and command a premium price," observes Helton.
For most devices, the jump from "ordinary" to N-I is minimal in terms of price and performance. But, the jump in price and performance from N-I to I-safe is substantial. "Specifying a device for use in Division 1 locations means more cost, more weight, fewer features, and less battery life. Repairs are more costly and may take longer due to availability of special spare parts, that is if the device can be repaired at all," observes Helton.
"Even over-specifying the gas groups needed for an I-safe device can cost you more and significantly limit the number of devices to select from. Qualification of devices for use in Division 1, Class I,Groups A and B is dramatically more difficult (read: This as more costly and has a reduced feature set) than qualification of the same device for use in Class I, Groups C and D," adds Helton.
"The single most cost-effective decision a company can make with regard to devices rated for use in hazardous locations is to not over specify the rating needed. Our input from various sources indicates that over 90% of hazardous locations in the U.S. are rated Division 2, which means that a N-I rating is sufficient," concludes Helton.
Are common portable electronic devices such as digital cameras, cell phones, and PDAs I-safe? Unfortunately, no such assumptions can be made. Ecom Instruments (www.ecom-ex.com) is one of the leading manufacturers of portable I-safe devices, and highlighted on their web site are an I-safe digital camera, an N-I cell phone, an I-safe cell phone, and an N-I Pocket PC.
Does this mean that similar and less expensive non-rated commercial products from are not safe for use in hazardous areas? It is impossible to tell. Many cell phones might pass N-I or I-safe tests, but few have been tested.
Besides a rated product, what else does one get for the premium price attached to I-safe devices? "I-safe products are usually ruggedized, which may result in a little extra weight, but rugged products tend to last much longer in process plants" says Markus Nied, the managing director of Ecom.
