This is another Top 10 question on flammable liquids safety I get from clients, cold calls, referrals, and friends. Most are familiar with the testing limits for path to ground on bonding/grounding stations of 10/25 ohms. In my previous post tonight I explained where these 10 and 25 ohm limits came from and how they are essential very LARGE SAFETY MARGINS for our systems.
When we look at NFPA 77 (2024) we see a very different and much larger number for a pair of Electro Static Dissipative (ESD) footwear…
NFPA 77, 8.2.2.2 states the following about ESD, or as NFPA calls them – SD footwear…
Static dissipative (SD) footwear used in conjunction with conductive or static dissipative flooring provides a means to control and dissipate static electric charges from the human body. Resistance to earth through static dissipative footwear and conductive or static dissipative flooring should be between 1 × 106 (1,000,000) ohms and 1 × 108 (100,000,000) ohms.
For materials with very low ignition energies, the resistance to earth through footwear and flooring should be less than 1 × 106 (1,000,000) ohms.
Resistance should be measured with commercially available footwear conductivity testers.
This is because 1,000,000 ohm (1 megohm) is the resistance where we lose the ability to manage static charges. If we are testing our ESD footwear DAILY and our flooring at least annually, then ESD footwear “passes” @ 1,000,000 ohms.