A Posting From Forum Moderator Ron Moore

In the University of Extrication seminars that I present, I still get funny looks and raised eyebrows when I recommend that BOTH the negative AND the Hot cables be cut or disconnected. Just cutting or disconnecting the negative cables ( what I call "partial" battery shutdown) on a vehicle's electrical system are not enough. I use the following NHTSA incident report to illustrate my point.

The National Highway Traffic Safety Administration (NHTSA) reported an interesting event that reinforces the need for total electrical system shutdown. A crash test was conducted by GM engineers simulating an impact by one vehicle into the left front corner of another vehicle with a closing speed of 65 mph. As fire department members approached the crashed vehicle to inspect for post-collision fire, officials noted that the battery had broken open and smoke was rising from it. The negative battery cable was then disconnected by firefighters.

Several minutes later, an observer noticed that the vehicle's tail lights appeared to be "on". Closer analysis revealed that in fact the tail light bulbs were illuminated. It was discovered that a sheet-metal screw had penetrated the side of the battery during the collision, creating a new ground circuit for the electrical system. Even though the battery was severely damaged during the crash, the ground cable completely disconnected and three of its six internal cells without any battery acid, the battery still generated approximately 7.5 volts of energy. The power and heat generated by the electrical current flowing through this unfused circuit were sufficient to light the vehicle's tail lights and to start a fire in the vehicle.

Totally shutting down a vehicle's electrical does not insure that a loaded airbag will not deploy during our extrication. Disconnecting the battery early in our rescue activities is, however, the most effective means of minimizing the potential for loaded airbag deployment.

Vehicle rescue is still a gamble against time for both the patient and the rescuer. By aggressively shutting down the vehicle's electrical system, as professionals, we are simply minimizing our risks.

Partial battery shutdown is unacceptable!

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