Lightning, Flammable Atmospheres, and the Cost of Getting Earthing Wrong

In most sectors, a lightning protection failure costs money. In oil and gas, it can cost a great deal more. When the thing you are protecting is a structure full of flammable vapour, the protection system is not just guarding equipment, it is one of the layers standing between a lightning strike and an ignition. That changes the engineering, the tolerances, and the consequences of getting it wrong.

The uncomfortable truth in this sector is that lightning does not have to start a fire to cause one. It only has to create a spark in the wrong place at the wrong moment. Here is where those moments hide, and why the earthing and bonding standard in a hazardous area is set so much higher than elsewhere.

The hazard is the spark, not the strike

A direct lightning strike to a process structure is the obvious danger, but it is not the most insidious one. The more subtle risk is a small, secondary spark produced somewhere on the facility by the lightning event: across a poorly bonded joint, at a high-resistance connection, or between two metallic parts that the strike has briefly raised to different potentials. In an ordinary building, that spark is harmless. In a classified hazardous area, where flammable vapour may be present, it is a potential ignition source.

This is why bonding matters more here than almost anywhere else. Bonding ties all the metallic parts of a facility together so that when lightning current flows, everything rises and falls in potential together and no dangerous voltage differences open up across a gap. The goal is to remove the conditions in which a spark can form, not merely to carry the main strike to earth.

Why hazardous-area bonding has to be far tighter

Here is a distinction that catches people out. The bonding resistance considered adequate for draining static electricity is not adequate for lightning. Static charges are small, and a relatively high-resistance bond, up to around a megohm, will safely dissipate them. A lightning discharge is orders of magnitude larger, and a bond that comfortably handles static can still develop a dangerous voltage across it under lightning current.

This is the kind of detail that separates expert hazardous-area work from general electrical practice. A bond is not simply present or absent, it is adequate or inadequate for the energy it has to handle, and lightning sets the demanding end of that scale.

The floating-roof tank: a worked example of the risk

Aboveground storage tanks with floating roofs are the textbook case, because the ignition path is so specific. The seal between the floating roof and the tank shell relies on metallic shoes maintaining a low-resistance connection to the shell. When that connection degrades, and measured resistances across these joints have been found in the range of millions of ohms where they should be near zero, a lightning event can drive an arc across the seal, directly into the vapour space at the rim. The result is a rim-seal fire.

The petroleum industry's own data has long attributed a substantial share of large storage-tank fires to lightning, with rim-seal ignition a recurring mechanism. It is a sharp illustration of the general principle: the danger is rarely the headline strike, it is the unmanaged secondary path that the strike energises.

The standards that govern it

Hazardous-area lightning and ignition protection sits at the intersection of several standards, and a competent design has to satisfy all of them together:

• API RP 2003 (Protection Against Ignitions Arising Out of Static, Lightning, and Stray Currents) is the core petroleum-industry reference for the ignition mechanisms themselves.
• API RP 545 addresses lightning protection of aboveground storage tanks for flammable and combustible liquids specifically.
• IEC 60079 / AS/NZS 60079 governs the classification of hazardous areas into zones, which determines what is permitted where.
• IEC 62305 provides the overarching lightning protection framework, applied with the sector's additional constraints.

Zone classification is the thread that runs through all of it. Every protection component, every surge device, every bonding detail within a classified area has to be appropriate for the zone it sits in. A solution that is perfectly sound in a safe area can be non-compliant, or unsafe, a few metres away inside a Zone 1 boundary.

Where this leaves an operator

The consequence profile in oil and gas does not tolerate the assumptions that pass elsewhere. A bonding connection that was adequate for static, a seal that has quietly corroded, a surge device rated for the wrong zone: each is a small thing, and each can be the difference between a lightning event that passes harmlessly and one that does not.

Our oil and gas protection work integrates lightning and earthing design with hazardous-area classification and existing bonding and cathodic protection systems, rather than treating them as separate problems. That integration is the point: in this sector, the lightning protection system and the ignition-prevention strategy are the same strategy. Verifying that bonds still meet the lightning standard, not just the static one, is exactly the kind of thing a periodic site audit and earthing test exists to catch, before the weather does.