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FIRE FROM THE SKY
Special protection zones leave Chad facilities strike free in reputed lightning capital of the world
Volume 22, No. 6

With dwindling world oil supply and increasing demand as economic powerhouses like China and India continue to grow, petroleum sourcing is expanding into high lightning-risk areas such as parts of Africa, Asia and South America. To meet demand, companies have had to explore alternative methods of protection to maintain 24/7 production, despite the elevated lightning risk. In place of antiquated lightning rods that actually attract lightning to a site, a growing number of respected petroleum companies are turning to engineered "zones of protection" to avoid lightning-related equipment damage and unscheduled downtime.

In the heart of Africa, the Chad/Cameroon Development Project opened a revenue stream a few years ago with the completion of an estimated one-billion barrel oil field in Chad and a 663-mile pipeline through Cameroon to an offshore marine export terminal.

To meet market demand and protect production, one oil production operation in Chad had to proactively consider how to protect its facilities from lightning risk. Where an isokeraunic number of 30 indicates average lighting activity of about 13.7 strikes per square mile annually, the region developed by the oil production operation has an isokeraunic number of 120, indicating about 41 annual lightning strikes per square mile.

"Chad has some of the most intense, most frequent lighting strikes in the world, with about two lightning storms a week from mid May to early October," said an electrical engineer for the oil production operation in Chad. "Still to meet demand and production goals, we have to stay up and running without unscheduled downtime."

To sufficiently protect its facilities, including a central processing site and three outlying gathering sites, the oil production operation decided against using traditional lighting rods, which are designed to attract lightning.

Instead, the oil production operation opted to proactively protect its central processing site and three outlying gathering sites, using the expertise of Lightning Eliminators and Consultants, Inc. (LEC), a Boulder, Colorado-based leader in lightning prevention technology, to engineer "zones of protection" for each facility.

For the oil production operation, LEC custom engineered, designed and deployed interconnected systems for strike prevention and low impedance grounding, utilizing its Dissipation Array System? (DAS?).

DAS, a charge transfer technology that's being lauded as a comprehensive, preventive solution for modern lightning protection, essentially prevents strikes by continually lowering the voltage differential between the ground and charged storm clouds to well below lightning potential. In the US and abroad, DAS has proven to be the preventative solution for lightning protection, substantially cutting storm-induced voltages as compared to the unprotected surroundings, thus eliminating the lightning strike risk.

Since it prevents, DAS is often the best long-term solution to lightning strike problems.

In order to protect about 1.25 square miles of facility space -- including the central site encompassing about 0.5 square miles, and three separate gathering sites encompassing about 0.25 square miles each -- LEC took into account factors such as each facility's location, size, shape, equipment, geography and exposure to lightning activity.

To discharge structures of the voltage differential between the ground and charged storm clouds, DAS was deployed in various configurations across the protected sites. Stack arrays were used to protect turbine generators, which have protruding exhaust stacks.

U-bracket arrays were used to protect buildings or structures with architectural or weight restrictions. Hemisphere arrays were used to protect a telecom tower and high-mass lights for night illumination.

While rim arrays were used to prevent lightning strikes to floating roof storage tanks, multiple Retractable Grounding Assem-bliesTM were deployed to prevent arcing at the gap between the seal of the floating roof and the tank wall, caused by lightning storm and ground current activity. The RGA, a device that provides a direct connection to the tank roof from the tank wall, uses a wide, thick-braided wire cable wound on a heavy stainless steel reel, with tension held by spring loading. The path of impedance is kept to a practical minimum by the combination of the shortest path, wide braid and constant tension.

In addition, an ultra-low impedance grounding system was also necessary to transfer induced ground charges efficiently, since transient voltages such as lightning are affected by impedance while resistance pertains to DC voltage. An appropriate number, sizing and spacing of Chem-Rods, which use natural mineral chemicals to improve conductivity up to ten fold over traditional grounding rods, helped achieve a significantly reduced ground resistance with a target of less than one ohm. Reducing grounding impedance was important, as the natural soil resistivity at various sites ranged from less than 30 ohms near a riverbank to over 500 ohms up a sandy hill.

The result of such proactive protection of upstream facilities has been significant.

"With the engineered 'zones of protection' in place, not a single lightning strike has hit us in our protected zones, and it's been over three years now," relates one engineer. "Only once, when CCTV installers mistakenly put a camera above a protected zone, did it get struck by lightning. The CCTV camera was shattered. To me, it was quite a demonstration of the effectiveness of DAS."

While initially skeptical of the "zone of protection" concept, the engineer admits that he's a believer now. He considers the odds of the facilities not getting hit in their protected zones, in over three years, in one of the most active lightning spots in the world highly unlikely without the addition of the integrated lightning protection system.

In a region with an isokeraunic number of 120, indicating about 41 annual lightning strikes per square mile, the oil production operation's approximately 1.25 sq. miles of upstream facilities would be expected to have about 51 lightning strikes per year and over 150 in a typical three year period. Instead, the facilities have had zero strikes in their protected zones.

The net effect of this kind of lightning protection has been significant to the bottom line.

"If we didn't have DAS and the 'zones of protection,' we'd have at least 10 to 15 percent more downtime during our long lightning season," says the engineer. "I'd be working 24 hours a day fixing remote instrument enclosures, doing incident investigations on lightning strike shutdowns and the like. Instead, we're in production. That translates into tens of millions of dollars a year in avoided downtime and additional revenue."

 
 

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