The most insidious danger in fuel loading is invisible to the eye: as the liquid flows and rubs against pipe and hose surfaces, it accumulates electrical charge. This static charge built up inside the tank can discharge as a single spark under the right conditions; the spark's energy is more than enough to ignite fuel vapour.
Where and How Does the Charge Build Up?
Charge generation increases with flow rate; filters and pipe elbows accelerate generation by enlarging the friction surface. Filling the tank by free fall from above (splash loading) increases both vapour generation and charge separation, which is one of the reasons bottom loading is preferred. The charge inside the tank persists for a while even after filling ends; that is why post-fill waiting periods appear in procedures.
The Line of Defence: Bonding and Grounding
- The first task before filling: connecting the grounding clamp to a clean metal surface; a painted or dirty surface fools the connection
- Bonding (equipotential connection) between the tanker, the loading island and the pipeline: no potential difference means no spark either
- In systems with grounding-monitoring devices, filling must not start until the connection is verified
- Keeping flow rate, especially at the start of filling, within the limits defined in the procedure
- Daily inspection of frayed bonding cable, loose clamps and corroded connection points
On the design side, Barlas's approach is clear: grounding points must be accessible, marked and continuously conductively bonded to the shell. Static electricity is not an unmanageable fate; it is a risk that is zeroed out through discipline.