Electricity + Control

On 7 October 2017, a lightning strike caused a major fire in an oil storage tank on Butcher Island (Jawahar Dweep), off the Mumbai shore. It took four days to extinguish the fire on the island, which houses a marine oil terminal of the Mumbai Port Trust, where oil tankers discharge crude oil, thereafter transported to refineries through submerged pipelines.

Following an investigation, India’s Oil Industry Safety Directorate (OISD) found serious lapses in procedure and protocol. One point mentioned was that the roof plate thickness of the tank was less than 4.8 mm and thus able to be punctured by the lightning strike, allowing the fire to be ignited.

This kind of disaster attests to the critical necessity of making sure that flammable substances, which may present potentially explosive atmospheres, are protected from the possibility of lightning currents and surges.

According to Julienne Puttkammer, part of the technical team at DEHN AFRICA, this is a very illustrative example of how badly things can go wrong when lighting strikes a potential explosive zone that is not adequately protected. “The strike at Butcher Island followed the usual expected scenario when the tank’s contents burned rather than exploding, incurring huge costs. Fortunately, there was no loss of life.

“It’s not surprising that anywhere flammable substances such as fuel, alcohol, liquid gas and explosive dusts are produced, processed, stored and transported, could potentially be an explosive atmosphere. Essentially, temperature differences where flammable liquids are stored can create fumes within the storage facility, and then if this area becomes too warm, it can be ignited, or even explode. Similarly, when it comes to flammable powders, static can cause friction in the fine particles of the powder, which could then catch fire. Part of the reason that the Jawahar Dweep fire burned for so long is because reignition of the fuel – due to the extreme heat – kept the blaze going.”

To ensure the safety and availability of a chemical or petrochemical plant, procedures are required to protect the tanks from a direct lightning strike, as well as electrical and electronic installations from lightning currents and surges that could be the cause of an explosion. As Puttkammer explains, “The point is therefore to prevent sparking and ignition of these explosive atmospheres, particularly at oil depots, fuel stations and biogas tanks, where biological waste and fermentation processes create the gas that is used for energy sources. The simplified science is that if something is used for energy, it is often explosive or flammable.”

Puttkammer says petrol stations and storage depots are governed by stringent regulations around protection from static sparking and lightning strikes. “The electrical systems in these zones must be housed in special explosive proof piping and enclosures to isolate any potential sparking and must be designed to prevent any heating of the conductors, known as intrinsic safety, so that even in a worst case scenario, the stored fuel in the area will still be safe from ignition. This is a big part of managing the lightning risk. Furthermore, if fuel tanks are exposed to direct lightning strikes or not made of adequate housing to be safe in the event of a direct strike, the threat, as illustrated by the Jawahar Dweep fire, would be virtually unmanageable. Therefore, the earthing, lightning protection and equipotential bonding precautions are critically important.”

DEHN AFRICA, the local subsidiary of DEHN, a globally active electrotechnical company offering comprehensive services, products and solutions in the field of surge protection, lightning protection and safety equipment, has wide experience in protecting explosive (EX) zones in South Africa and other African countries, and has also worked on projects in Indonesia, Singapore and Australia.

“Mines, for example coal mines, have EX zones because of the fine particles of dust on site that can cause a flare-up. We have also been involved in the protection of a biogas plant in Indonesia, as well as another renewable energy plant in South Africa that was a hybrid of biogas and solar power. Additionally, we have been involved in a few designs for the installation of protection at petrol stations and depots in South Africa for a number of local brands.”

Puttkammer explains that if lightning were to strike directly, the direct strike point has to be calculated in accordance with any EX zones “The EX zones are normally defined by a specialist, and different areas are attributed different properties of how much vapour or dust is expected in hours over a period of a year. The zones are named 0/20, which is generally inside a tank close to the fuel; 1/21, an area with a more regular vapour release, for example a vent; and 2/22, for example an emergency vent. When DEHN is informed about the areas in a plant, we can design the lightning protection and equipotential bonding to make sure there is a greatly reduced risk of sparking or heating of metallic parts in these areas.”

DEHN has a number of products that are specifically designed and tested for explosive zone applications, he says. “They are tested and given stamps of approval for working safely within the 1/21 and 2/22 EX zones. We are also able to create specialised solutions that suit specific requirements of certain industries, for example around temperatures and connection points. Whereas in the past, lightning protection used free-standing masts away from the storage tank, today we have advanced isolated systems that can safely be mounted on the tank itself. Our specialised solutions could also involve having a normal mast bonded to the tank, following all the required calculations and selections, as a less intrusive method for tanks that are in operation and which you couldn’t weld or drill into.”

Standard DEHN products and solutions that are specifically designed and tested for explosive zone applications include DEHN’s advanced HVI® isolated lightning protection systems, as well as EX zone pipe clamps, isolating spark gaps and surge protection devices. DEHN AFRICA offers the services of lightning risk assessments, done as an initial step, followed by detailed designs which may include lightning protection system temperature rise analysis, installation safety reports and all required soil surveying and system testing involved from beginning to end.

“Potentially explosive zones are closer to us in everyday life than we might realise, and of course vast areas of South Africa, especially at particular times of year, have high lightning flash densities when compared to many other places in the world. Take comfort, the next time you fill up your car at a fuel station, that the garage is built to follow South African and international lightning protection standards and must be highly protected from the chances of catastrophe due to a lightning strike,” concludes Puttkammer.

Enquiries: Tel. +27 (0) 11 704 1487

 
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