Over the years there have been a number of in-flight smoke and fire events where contaminants ignited by electrical faults allowed the fire to be sustained and spread. The FAA and the National Transportation Safety Board (NTSB) have conducted aircraft inspections and found wiring contaminated with items such as dust, dirt, metal shavings, lavatory waste water, coffee, soft drinks, and napkins. Sometimes wire bundles and surrounding areas have been found to be completely covered with dust.
 
In recent years both the FAA & Industry have realized that current maintenance practices may not be enough to address aging non-structural systems. Over time, insulation can crack or breach, thus exposing the conductor.