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LDRD report: Smoke effects on electrical equipment
Smoke is known to cause electrical equipment failure, but the likelihood of immediate failure during a fire is unknown. Traditional failure assessment techniques measure the density of ionic contaminants deposited on surfaces to determine the need for cleaning or replacement of electronic equipment exposed to smoke. Such techniques focus on long-term effects, such as corrosion, but do not address the immediate effects of the fire. This document reports the results of tests on the immediate effects of smoke on electronic equipment. Various circuits and components were exposed to smoke from different fields in a static smoke exposure chamber and were monitored throughout the exposure. Electrically, the loss of insulation resistance was the most important change caused by smoke. For direct current circuits, soot collected on high-voltage surfaces sometimes formed semi-conductive soot bridges that shorted the circuit. For high voltage alternating current circuits, the smoke also tended to increase the likelihood of arcing, but did not accumulate on the surfaces. Static random access memory chips failed for high levels of smoke, but hard disk drives did not. High humidity increased the conductive properties of the smoke. The conductivity does not increase linearly with smoke density as first proposed; however, it does increase with quantity. The data can be used to give a rough estimate of the amount of smoke that will cause failures in CMOS memory chips, dc and ac circuits. Comparisons of this data to other fire tests can be made through the optical and mass density measurements of the smoke.