Do such tags pose any ignition hazard, and has testing been performed to determine whether they can be dangerous?
The ATEX Directive, which became mandatory in Europe in 2003, dictates that all electrical and mechanical equipment used near explosives or explosive fuels or gasses must be certified as safe. That is, they must be tested to ensure that a product cannot produce a spark that will ignite an explosion or fire.
It is up to individual tag manufacturers to submit their products for approval, and some have done so. For example, The Tag Factory's M-Nano and M-Crown tags are ATEX-approved, according to the company's Web site.
Most passive ultrahigh-frequency (UHF) tags have not yet been submitted for approval, but I know that the U.S. Department of Defense (DOD) has tested passive tags to ensure that they cannot ignite explosives. The DOD defines these tags as HERO-compliant (HERO stands for Hazards of Electromagnetic Radiation on Ordnance).
I reached out to Victor Vega, NXP Semiconductors' director of RFID solutions, to get his views on the topic. Here's his response:
"The Europe directive is fundamentally equivalent to the Intrinsic Safety directive in the United States. Intrinsically safe equipment is defined as 'equipment and wiring that 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.' For passive tags harvesting RF energy from a reader, internal storage is very limited (the capacitive reserve is typically less than 1mF, and inductance is typically less than 10nH). And since passive UHF tags do not comprise internal power sources, and considering that the maximum voltage levels at the antenna terminals is typically less than 1V and the maximum internal current is typically less than 1mA, it suggests that typical UHF IC operating characteristics are significantly lower than those for intrinsically safe circuits."
Victor stresses that he is not saying it is okay to use all passive UHF tags in the presence of explosive gases or fuels, but rather that it's likely that tags submitted for ATEX approval and testing will likely be certified as safe. If you have plans to use a specific tag in an area covered under the ATEX Directive, please make sure the supplier has submitted that tag for ATEX approval.
—Mark Roberti, Founder and Editor, RFID Journal