Note: This is a sidebar to the January feature, "Intrinsic Safety: Thinking Outside the Explosion-Proof Box."
These days, it’s not that difficult to pick out integrated safety devices because most follow standards and generally the same specifications. There are different but similar IS standards around the world, so you should be aware of what you’re looking for.
Although you might check that your instruments have the proper ratings for your geographic location, there’s a bit more to look for. “They need to actually get in and look and verify that it has the ratings for the area that they’re going into, like Class I, Div. 1, or a zone environment,” explains Robert Schosker of Pepperl+Fuchs.
In North America, the categorization of hazardous areas is done in accordance with NEC article 500. “Class tells you if it’s gas or dust; division tells you the probability of the hazard being present; and group tells you the type of hazard,” says Randy Durick of Turck.
Class I, Div. 1 areas contain dangerous concentrations of flammable gases, vapors or mist continuously or occasionally under normal operating conditions. “If I want to run pressure measurement with an analog device at 4-20 mA, I could make it explosion-proof,” Durick says. “But it opens up the opportunity for intrinsic safety instead.”
Europe operates more according to a three-zone model. Zones 0 and 1 line up most directly with Div. 1, but not exactly. Zone 0 is the most dangerous, and any instrument used there must be incapable of having enough energy to ignite a fuel mixture.
“We try to design devices to comply with all the IS standards; all the global IS requirements,” says Roberto Zucchi of ABB. This makes it easier for the supplier to create devices that can fit everywhere, but might not be important to the user. “If he knows where the project is going to be located, he doesn’t care if it has all the international standards,” he adds.
You should also make sure that the instruments you buy are approved by a third party like FM or UL in the U.S., or ATEX in Europe.
The decision about what type of safety to go with—whether IS, explosion-proof or another method—could well be dictated by your insurance provider, according to Ted Dimm of Honeywell Process Solutions. “The insurance company that you’re dealing with has probably vetted that decision and supports that decision,” he says. “They have to understand and know what that’s all about.”