Archive for June, 2011
Q: Can a facility technician wearing an ESD safety shoe pose a risk of electrocution?
The manufacturing area is grounded with a dissipative mat with a resistance of 10^7 ~ 10^8.
A: You would be more prone to electrocution with ESD footwear on than not. This is because ESD Static Dissipative and ESD Conductive footwear are designed to protect static sensitive devices and prevent the initiation of ordinance/munitions/explosive powders, gases, liquids etc. respectively… but with a lower threshold resistor to prevent defibrillation.
When wearing such footwear, you do not want to expose yourself to open line voltages… just as the case when wearing insulated footwear. Be particularly careful of line voltages of 110 and above.
DoD 4145 26 M deals with explosive environments and the control of ESD in such environments, as well as NFPA 77. For protection of ESD sensitive devices, consult ANSI/ESD S20.20-2007. The former has requirements for a lower threshold of ESD work surfaces to be above 40,000 ohms for 110 systems and 75,000 ohms for 220 systems, but no such lower threshold for footwear, that I’m aware of. They do have a combined resistance requirement of less than 1E6 ohms or a meg ohm for body, footwear, and flooring to ground in the case of ESD Conductive footwear.
For ESD Static Dissipative footwear, the upper limit is 3.5E7 ohms or 35 megahoms, and the lower limit is at some fraction of a meg ohm… I guess that would be set by your ESD footwear/wrist strap tester.
Thanks for your question.
Patrick McGowan, EET
Director of Engineering/ESD Auditor
Ground Zero ElectroStatics, Inc.