The Landfill Gas Explosions which Shocked the UK's Waste Management Industry into Action
The waste management industry learnt by hard experience the risks imposed by the generation of landfill gas in their landfills, and the penalties in terms of death and injury.
Somehow, although the parallel experiences were there from the start in the mining industry, for the landfill operators to learn from, (and the terrible death toll from the water industry's Abbeystead Explosion in the 1970s was well known), it took several explosions before operators and regulators took action.
Thankfully, with current greatly improved landfill practices, accidents of the type described here have become a thing of the past.
We describe below some of the most well known and influential incidents which to a large extent shaped the UK Environment Agency's landfill development requirements and gas migration prevention guidance, until the advent of the EU Landfill Directive in the late 1990s, as now embodied in the the EU ATEX Directive (and UK's DSEAR regulations).
Abbeystead Explosion, Cumbria
The explosion at the Abbeystead valve house on 23rd of May 1984 killed sixteen as a result of methane gas in the atmosphere. Although the methane is thought to have been from natural sources rather than landfill gas the accident provides a tragic example of the potential hazard posed by methane in pipes.
Loscoe Explosion, Derbyshire
An explosion occurred in a bungalow adjacent to the landfill site at Loscoe during March 1986, when a large fall in barometric pressure occurred (29 millibars in 7 hours).
The explosion destroyed one bungalow, and the resulting investigation showed two more houses had been unfit for habitation for the preceding nine months, and others for short periods.
The site was used as a brickworks from the mid-nineteenth century until the early 1970's, the quarry in which it was situated comprised an elliptical hole with three stepped quarry faces. The quarry was part filled with inert waste products from the brick making which ceased in 1971.
Permission was then granted for the tipping of inert materials only, and from 1973 to 1975 a number of companies tipped at the site, until one firm acquired the sole rights, and in 1978 purchased the site. During 1977 a licence had been granted to tip a wide variety of wastes, including 50 tons per day of untreated domestic waste.
From 1977 to 1982 amendments to the licence were granted to increase the quantities of domestic waste tipped, despite complaints from the residents of adjacent houses of vermin and flies. Houses surrounded the site on all four sides, those on the fourth side were built in the 1970's.
The first signs of gas generation were in 1984 when lawns and trees began to die in the surrounding gardens. Later the soil around the affected areas began to heat up. This is thought to be have been due to the presence of methane feeding bacteria.
After the explosion Derbyshire County Council monitored methane levels in the houses at regular intervals and attempts were made to draw the gas out of the tip by horizontal and vertical methane extraction wells. This proved only partially successful due to a perched water table (Open University literature 1989).
Flow rates of landfill gas generated from the site measured subsequently were 150-200 cubic metres of gas per hour at a 30-35% methane content, with 3-4% oxygen: or approximately 45-70 cubic metres of methane per hour. After the explosion this gas was extracted, and this was achieved by 17 wells, and the extracted gas was flared off through a purpose built pump and flaring unit.
North Yorkshire
A house 50m from a waste filled limestone quarry was seriously damaged by a methane gas explosion. The gas was generated from domestic and commercial waste dumped over a three year period and had migrated along natural fissures in the limestone underneath the house.
Precautions had been taken against gas migration as the site was filled including facing the quarry wall with clay and creating rubble 'chimneys' within the waste. These chimneys and a permeable cover material had however then become covered over in the final phase of operation.
There was no prior warning of the problem, but for four days after the explosion high concentrations of methane were found in the drains of the area. Other houses in the vicinity were checked for methane but only very low levels were recorded.
The remedial steps taken were to dig trenches into the waste along the rock faces and backfill these with imported rock graded 75-250 mm. Within two weeks of the trenches being excavated only trace levels of methane were recorded outside the site (County Surveyors Society,.1987).
Atlanta, Georgia, USA
In December, 1967 a single storey building was destroyed, two people killed and two injured by a methane gas explosion. The building had a basement which was bricked up sealing it except for a pipe which connected the basement to the rest of the building. Landfill gas escaping from the pipe was ignited possibly by a cigarette and an explosion occurred. (Parker.1987)
Winston-Salem, North Carolina, USA
In 1969 a gas explosion occurred in an armoury built close to a landfill site. The building was erected seven years earlier when the site was operational, but about a week before the explosion extra material was deposited over the site and it is thought this caused the gas migration into the building. The explosion killed three people, and twenty five were injured (Parker, 1987).
In these accidents the explosion was caused by alterations to the pathways for gas migration after the closure of the site. These alterations or blockages caused the landfill gas to accumulate in an enclosed area and reach an explosive limit.
Therefore the problems associated with landfill gas both in the gaseous phase and dissolved in landfill leachate are a long term explosion risk which must be carefully assessed and managed.
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