A few weeks back, I was assisting an HTM service professional in the field with a problematic medical device issue that was being troubleshot. As we conversed about the service event, I had asked if power had been disconnected prior to a part replacement that was performed and suspected as now being defective. The HTM service professional said the medical device power was turned off at its control console. I asked if power could still be present at any other location in this medical device’s system configuration. The HTM service professional replied, “Doesn’t flipping the on/off switch at the operator console kill the power everywhere?” The answer is most times NO! As in this medical device’s case that was true, though the operator console switch was in the “off” position, power was still present at several location within the system and subsequently had taken out the new replacement part. A very expensive replacement part I may add as well that required re-ordering and more “downtime” to a very critical medical device. The customer was not happy!
Assuring power may be present or has fully been removed from a medical device when required for troubleshooting or parts replacement is not only critical in the repair process but more importantly a significant safety practice. Electrical shock either from alternating current (AC) or direct current (DC) can be not only harmful but deadly. 30+ milli amps of AC or 300+ milli amps of DC can cause fibrillation and lead to cardiac arrest. As little as 10 micro amps across the chest constitutes micro shock and can induce defibrillation to occur and lead to cardiac arrest. High voltages starting at 500 volts and up can cause deep tissue heating and internal burns in micro seconds!!
Being cognoscente of the power presence around any device, big or small, that you may be performing service to is a crucial safety practice. The actions in assuring a state of safety are quite simple. Identifying the power source(s) pathways and disconnects of the device can be derived by reading the schematics and service manual. Following lock-out and tagging procedures is a must. And when in doubt put a meter on its first before your finger!
