Mobile Static Earthing System
Normally, road tankers (tank trucks) load/unload at a fixed point in a factory. However, vacuum trucks can work anywhere from main roads/highways to refineries/chemical plants and require a different grounding solution.
Continuity between all metal parts on the vacuum truck is essential. Every metal item must be bonded to the chassis and tank with caution towards paint, coatings and hose trays.
The most crucial aspect of safety concerning vacuum trucks is the education of the operator that on arrival at site they attach the grounding clamp first and get a GREEN flashing LED that clearly shows that the truck is grounded before any other operations are started e.g. attaching hoses.
The second most crucial part is to remove the clamp after all other operations have been completed and equipment packed away – clamp on first and clamp off last.
A lot of users fit a simple hand wound or retractable cable reel and clamp to protect vacuum trucks and road tankers. The advantage to installing a monitored grounding system will alert users of the following dangers:
- The grounding system will provide a visual indication of a GOOD or BAD ground connection.
- The grounding system will provide true earth verification e.g. is the system connected to an earth that is capable of dissipating static electricity.
- The grounding system is a monitored circuit and will automatically shut down the product transfer if the ground connection is lost. However, the product itself would need to stop moving in order to prevent any further charge generation.
The grounding system complies with International Standards e.g. <10 Ohms metal to metal loop resistance between the teeth of the clamp and the chassis/tank of the vacuum truck.
Depending on construction, grounding clamps supplied by an intrinsically safe (ia) signal can go anywhere in a hazardous area/location (Zone 0 / Class I, Div. 1).
Depending on construction, grounding clamps supplied by an intrinsically safe (ib) signal can only go into a hazardous area/location (Zone 1, 2 / Class I, Div. 2).
A high intensity coloured light can be placed on the top of the truck and interlocked with the grounding system. This supplements the grounding system and allows the driver and all other team members to clearly see the condition of the grounding system and react accordingly.
If the vacuum truck often visits a remote loading site then it is good idea to get a verified grounding point installed and checked regularly by a responsible person. Rods in the ground are normally a good way of providing this designated grounding point.
If the vacuum truck rarely visits the remote loading site then a fully featured truck mounted grounding system will be required to let the driver test metallic objects installed in the earth near to the transfer point to see if any are suitable for use as a grounding point and therefore protect the product transfer, plant and personnel.