Archive for January, 2011
Q: We are making some highly explosive materials for Military use and need to test the operators body resistance before walking into our work areas to ensure there P.P.E. (Personal Protective Equipment) is right.
Assumed Operation of a device:
- Operator stands on a metal pad that is on the floor.
- Push a metal button that is on the wall with there finger.
- The unit gives a Green light to indicate pass (0 to 1M ohm).
- Or if a fail a Red light, above 1M ohm.
- It would also be good to have the resistance valve display as well, either via a digital meter or an analog meter.
The resistance values have to be 0 to 1M ohm.
Do you have any products that will do this or can you modify one of your existing products to do this?
A. Before answering your question I must point out that I disagree with your lower limit. To be less than 1e6 ohms is right, but to be less than about 5e5 or 500,000 ohms is incorrect.
It’s not safe for the personnel due to electrocution risk and heart defib, not to mention that it is outside of the realm of providing a soft-ground to charge dissipation. We want to neutralize charges to a safe level, but not too quickly. The energy being dissipated to earth that quickly would defeat the purpose of eliminating the spark that you are trying to avoid.
According to DoD 4145.26-M C22.214.171.124.1 on page 92, (Test criteria for Testing Conductive Footwear, Floors, and Tabletops), the maximum resistance of a body, plus the resistance of the conductive shoes, plus the resistance of the floor to the ground system shall not exceed 1,000,000 ohms total. That is, if 500,000 ohms is the maximum resistance allowed from the floor to the ground system, then 500,000 ohms is the maximum combined resistance allowed for the person’s body plus the resistance of the conductive shoes. The contractor can set the maximum resistance limits for the floor to the ground system and for the combined resistance of the person’s body plus the shoes, as long as the total resistance does not exceed 1,000,000 ohms.
In other words, if you use ESD Conductive shoes (see the HK-4327-TN) on an ESD conductive floor, you will meet this requirement. You might even meet this with SD shoes, but I would not risk it. I would use the conductive shoes and you should pass the tester without getting a fail for high or a fail for being too low.