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Some 159,000 turkeys are being gassed to contain an outbreak of bird flu in the UK. But how do you dispose of that many birds?
The carcasses are being rendered
When bird flu outbreaks caused panic in parts of South East Asia a couple of years ago, millions of animals were culled by being thrown, alive, on burning pyres, or were buried alive.
In Britain, where vets confirmed an outbreak of bird flu at a poultry farm near Lowestoft in Suffolk over the weekend, the means of extermination is more humane.
The H5N1 virus can be fatal if passed on to humans, so as a precaution the slaughter of nearly 160,000 turkeys has begun at the Bernard Matthews farm in Holton.
It's very difficult to kill so many birds, says virus expert Professor John Oxford. Not only does the sheer number pose difficulties, there is also the risk of those doing the job getting infected.
So how do you get rid of so many birds safely?
Firstly, the birds will be gassed. Mobile gas chambers were delivered to the Holton farm over the weekend. All 159,000 turkeys will be placed into crates, "forklifted" into the chambers and gassed to death.
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It is the quickest, most bio-secure and humane method of killing the birds, according to the Department for the Environment, Food and Rural Affairs (Defra). The process is expected to take several days.
The carcasses will then be transported in sealed, leak-proof lorries to a rendering plant in Staffordshire. Each lorry has metal covers which are locked before leaving the farm. The vehicles are also cleansed and disinfected once outside the site.
Rendering involves the crushing and grinding of carcasses into a sludge, followed by heat treatment in a sealed vessel to reduce the moisture content and kill micro-organisms. Around 60% of the carcass weight is moisture and this is lost as steam.
Steam and gaseous emissions are collected, condensed and either bio-filtered - a technique using living material to filter or chemically process pollutants - or incinerated in a boiler. The process produces few direct emissions and any residue left over is disposed of in a landfill site.
A range of options are available for the disposal of carcases but rendering is the preferred method in this case as it is the safest way to ensure the virus is completely destroyed, says Defra.
The virus has killed 2,600 turkeys
Also, the chosen rendering plant is much larger than normal incineration plants and therefore has the capacity to deal with the large number of birds in this case.
There is a risk that those involved in the process could become infected. As a precaution they have been issued with personal protection equipment and are being offered the Tamiflu (human influenza) anti-viral drug.
There is no health risk from the burial of the residue in landfill as it is free from disease and the virus is no longer present, say Defra.
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