A grave event has taken place on December 3, 2020, at Avonmouth, Bristol, where eyewitnesses reported a massive three-second blast at the Wesset Water’s anaerobic digester. Unfortunately, the explosion killed four people working at the facility, and one more was severely injured as a result. The first photographs of the aftermath show a silo with a damaged upper section, a clear indication of pressure build-up.
Currently, experts are investigating the cause of the accident and the police are trying to ascertain the exact circumstances. This is very important because anaerobic digesters are widely used in the country and are considered generally safe. If there’s a design flaw or an operational error that happens to be a common practice in the field, it needs to be determined quickly.
These digesters are fed with waste from the top, and the methane that is produced is collected from the bottom. Methane is flammable and explosive, and this is the main reason for collecting it as it’s fuel. However, it can only light up in the presence of oxygen, which is why anaerobic digesters are designed to keep the atmospheric air out, as their very name suggests.
It is possible that a spark on the top of the silo caused the explosion as the workers may have been carrying out drilling operations or some other form of “hot work” at that moment. As witnesses don’t report fire or smoke, the scenario of the over-pressure building at the top section just under the lid gains ground, but a wide spectrum of possible explanations is still open.
A spokesman of Wessex Water has assured the local community that they are running no risks due to this incident and that the biosolids used in these silos are “treated sludge”, a by-product of the sewage treatment process. Thus, there have been no dangerous chemicals released in the air or anything that would cause health concerns.