Any anaerobic digester plant explosion is one too many.
Thankfully, nobody was hurt by this biogas explosion, thankfully. However, this does serve to emphasize that these very real risks that exist in anaerobic digestion.
Plastic membrane covers are normally comparably safe as they tend to deflate in the event of a small gas leak, and don’t provide a rigid void with part air and part methane present, which is of course much more likely to become an explosive mixture of methane and air within, what are called “the explosive limits!”.
A little bit of gas in air will burn and not explode, equally a methane filled space containing no oxygen will not explode, rather it would put out a flame.
Between these concentrations there is the explosive zone. In Europe a set of regulations known as the ATEX Regs. applies to assessing and managing explosion risks of this sort.
“EPDM” (ethylene propylene diene monomer (M-class) rubber), is the extremely durable synthetic rubber roofing membrane which is used to cover biogas tanks.
Now having given you the background, the original article link, and our extract from the article about this anaerobic digester plant explosion follows:
“The chances of an anaerobic digester exploding are slim to none. But that’s exactly what happened at Tim Bielenberg’s Oak Lea Farm in Aumsville, Ore. “I don’t …”
“The gas that was in that headspace combusted rather than going down the gas train to the engine or any other location. During that process, you have to have the exact combination of ambient air and methane for it to be combustible. It came in contact with some ignition source.”
“Fortunately, the system operated as designed so it began to shut itself down after the dramatic change in gas pressure and flame arrestors on the biogas train also proved effective. The minor damage was only above the rim of both tanks, and no one was hurt in this anaerobic digester plant explosion. While the chances of this happening again are rare, RES has taken steps to prevent “There are tremendous ground fields around the engine and the interconnection,”
“We ground the tanks, and we now apply a ground application to the EPDM as well.”
An Anaerobic Digester Plant Explosion Caught on Film
US Digester Plant Explosion in 1987
On February 6, 1987, two workers at a wastewater treatment plant were re-draining a sewage digester when an explosion lifted the 30-ton floating cover, killing both workers instantly. via www.cdc.gov
Sewage Biogas Plant Explosion in Madison 2016
The day of October 16, 2016 in Madison, Wisconsin began with thunder and lightning. As the employees of Madison Metropolitan Sewerage District arrived at work, lightning struck the fiberglass enclosure of their pressure regulator and flame-arrestor on top of the digester. A fire was sparked and quickly grew with heat intense enough to melt the lead weights in the pressure regulator. This whole time the digester was operating and generating highly flammable methane gas.
Employees were evacuating the area as the fire was extinguished, but the big event they were all bracing for never happened. There was no explosion! So many anaerobic treatment facilities have had explosions in the nearly the same situation.
Fires and explosions associated with anaerobic digesters and methane storage systems are more common than people realize, mostly because of widespread under reporting. This is especially true in “near miss” situations, where there is no human injury or death. via teamaquafix.com
Explosion and Fire at the Southwest Wastewater Treatment Plant in Springfield, MO
Two contract workers were injured after an explosion and fire Monday at the Southwest Wastewater Treatment Plant in Springfield, MO, the Springfield Fire Department said in a release. Fire crews responded to the municipal facility at about 4 p.m. Describing the incident as a “low order explosion with flash fire,” officials said a digester tank at the facility received damages and partially collapsed.
A group of three contractors were reportedly performing work on the digester tank at the city-owned facility when the explosion and fire occurred.
“They were working on the roof of this digester that had been emptied out,” Springfield Fire Battalion Chief, Heith Aldridge, told the Springfield News-Leader. “Apparently, there was a pocket of methane gas that was enough that, while they were working, it caught fire.”
The blast prompted the workers to jump from the top of the 15-ft tank. Two of the contractors received non-life-threatening injuries and were transported to an area hospital for treatment. via www.powderbulksolids.com
European Anaerobic Digestion Biogas Accidents
In Europe, there were about 800 accidents on biogas plants between 2005 and 2015. Fortunately, less than a dozen of them had consequences on human. Here are some examples.
In 2018, an explosion followed by a fire occurred at the level of the gasometer in the post-digestor of the farm plant in Saint-Fargeau, France. The accident happens during the initial test for the operation of the agitator when its propeller was replaced.
In 2005, a large quantity of H2S leaks in the charging hall of the biogas plant of Rhadereistedt, Germany. The workers don’t follow the procedure to discharge the truck because of a breakdown of the lid covering the tank. The tank containing animal and dairy waste is left opened. via www.biogasworld.com
Biogas risks include explosion, asphyxiation, and also on occasions also disease, and hydrogen sulfide poisoning.
Extreme caution is necessary when working with biogas. Adequate ventilation, appropriate precautions, good work practices, engineering controls, and adequate personal protective equipment will minimize the dangers associated with biogas.
Wherever possible, digester-associated tasks and maintenance should be performed without anyone having to enter confined spaces, including pits.
Systems should be initially designed so that confined space entry is not required to perform maintenance. via farm-energy.extension.org