CO2 Fire Extinguisher Produces Static Electric Shock
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Type:  Lessons Learned

Publisher:  Lawrence Livermore National Laboratory, Livermore, CA

Date: 

Topics:  Fire Protection, Compressed Gas/Air

During hands-on training with a carbon dioxide fire extinguisher, an employee experienced a static electric shock. The person described the sensation as, "A "solid" punch to the sternum and tingling sensations extending from both hands to just short of both elbows. The intensityof the tingling sensation felt similar to and slightly stronger than that experienced when shocked by household current. It subsided over approximately 20 minutes."

The extinguishers static charge increased until it could discharge itself to ground via the employee. The excellent electrical insulation of the high-top boots could have allowed up to 50kV to build up on the employees body over a few seconds of extinguisher operation. At that point, surface flashover across the outer surface of one or both boots is postulated as the mechanism of discharge. This would have dissipated the excess charge in less than a microsecond. Based on the human bodys capacitance, a painful shock would have been experienced across both arms (equally) and the trunk of the body as stored-up energy was dissipated. Although the voltage involved is high, as is the instantaneous current at breakdown, the current flows through and across the body for a very brief time and is not enough to endanger the heart or be life-threatening. In principle, this is similar to static shocks experienced from lower-current events, such as shoes shuffling across carpet. NOTE: Dry chemical fire extinguishers can experience the same charging while being discharged, but at a reduced rate compared to CO2 fire extinguishers.

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