Back in my HAZMAT days, we did a lot of transfers from damaged containers to proper containers to mitigate the release of hazardous materials. When the HAZMAT was a flammable liquid, we oftentimes had to construct our own grounding grid. This was more than not a massive challenge for us as we did this all over North America and the soils differ immensely depending on where we were operating and the time of the year. But these guys have put together this awesome video showing a method that I never used, but probably should have on several occasions. Tank trucks travel along roadways and along the roadways are many other buried utilities – so hammering an 8′ long copper rod into the ground comes with its own hazards and problems. These guys show us how to use a horizontal grounding field which is less than 12″ deep when we have concerns of buried utilities. The video is the best I have seen and the explanations provided are EXCELLENT. But take notice of this…
they could NEVER get their grid to 25 ohms or less; the best they achieved was 87 ohms and I loved that the instructor stated that they would have to REDUCE their transfer speed since they had a higher resistance to ground than what our speeds are based on (e.g. 25 ohms or less). I should also point out that NFPA 77 allows for the resistance of 1,000 ohms in HAZMAT situations:
7.4.1.3.1.1 In field-based situations such as HAZMAT hazardous response operations or flammable/combustible materials spill control and transfer, it might be necessary to establish a temporary or emergency grounding system in a remote location in order to dissipate static charges. In such situations, various types of conductive grounding electrodes can be used, such as rods, plates, and wires, which are sometimes used in combination to increase surface area contact with the earth. If the purpose of the temporary grounding system is to dissipate static electricity, a total resistance of up to 1 kohm (1000 ohms) in the ground path to earth is considered adequate. This can be measured using standard ground resistance testing instruments and is realistically and quickly achievable in most types of terrain and weather conditions.