22 July 2016
The chance of being struck by lightning is calculated as a one in 30,000 year event. Having been recently hit, Agrivert is pleased to report that we have survived without any injuries or damage to our local environment. So what happened and what lessons can be learnt?
At 5.20pm Thursday 16th June 2016 our Wallingford AD facility suffered a direct lightning hit during an unusual aggressive storm. The stirke ignited c.1200m3 of flammable biogas stored in the roof creating a spectacular 45 metre flare which was captured on camera by a local resident who was filming the storm (BBC News footage). This burnt out quickly leaving smaller fires burning until the roof membrane had burnt out. Most had self estinguished by the time the fire brigade arrived 15 minutes later.
The remaining digesters were still producing approx. 1000m3 of biogas/hour, so continuing to consume this as normal was the safest course of action. Once explained, the fire brigade teams agreed to allow restart of the CHP engines which had tripped as designed during the event.
Benefiting from more digesters than the industry average, we isolated tank 3, whilst using the others to keep operating. One of the isolation valves was heat damaged resulting in a slight gas leak which we sealed this within 3 hours; most of which was spent sourcing the appropriate parts which we didn’t hold in stock.
We ordered a new roof immediately, using the remaining 3 tanks to process normal feedstock volumes whilst we awaited its arrival. Normal waste acceptance was resumed the morning after the strike and we were back up to our usual 97% power output just 24 hours later. By day 14 repairs were completed and we were back to usual operating standards.
We draw two significant lessons:
Our extensive emergency plans are written for an internal audience.
- Simplifying these for an external audience could have expedited handovers to the fire crews and between their shifts/brigades.
- A more comprehensive array of seals in our stocks would have been an inexpensive way to expedite repairs and thus our recovery.
We are now reviewing lightning risk assessments at all sites but this is complex and there are various approaches to protecting a plant. In addition, on this occasion, the fire brigade’s opinion was that the lightning bolt missed 2 nearby taller metallic conductors but the sheer volume of rain water provided a conduit to our digester roof; demonstrating that the incident was largely unavoidable regardless of the type of protection we had in place.
In summary, whilst this was not a welcomed test, the experience has proved that our emergency procedures work well, the designed safety spacing of tanks works and our plants can remain safe and resilient; keeping our staff, the environment and the local community safe whilst providing continuity of waste acceptance and maintaining healthy power production in even the most unexpected of circumstances.
“I am very pleased with the outcome of what could have been a far more serious incident. Our staff performed fantastically, our customers, neighbours and regulators are happy and this can now become a great case study demonstrating the resilience of our plants” Alexander Maddan, Chief Executive.