Tuesday, July 29, 2008

Up one entry...

... and down another. Or in this case a badger sett - or rather an artificiallly created tunnel, above ground. We are gratefully to Trevor, Mr. Lawson of Badger Trust fame for pointing out that Defra have (allegedly) said:
" It was impossible to develop a reliable model for predicting whether humane concentrations of carbon monoxide gas could be achieved in a badger sett [4].
Please keep a close eye on that piece of verbal gymnastics - a single sentence from just one (of many) very long pdf file - as we summarise the work done in 2005/2006 by both Defra with one set of artificial sandcastles, or Porton Down with their very own bucket and spades .

Both were looking at reaching an optimum level of 1 percent concentration of carbon monoxide (CO) for long enough to euthanise the tunnel occupants without any visble side effects. Both used (different) models to predict concentrations, and a number of 'assumptions' were made in order to construct the model. Neither factored in animal movement, and thus movement of air / gas within the chambers.
In Defra's paper (No 2 on the list)
Target concentrations were exceeded 13m from the entrance in all trials and sustained for 24 hours when tunnel entrances were blocked - in all conditions. The trials achieved concentrations of CO thought to be sufficient to kill badgers.
Porton Down repeated this exercise in paper 4 with the same results. They may even have used the same delivery vehicle. Defra appear to have located an 18 year old Rangy 3.5l petrol automatic, which they are at pains to point out would have failed its MOT on emmissions and couldn't be transported legally on the public highway. Did it have a SORN declaration, one wonders? They continue:
"In all four trials CO concentration exceeded 3 percent after 60 - 80 minutes, and stayed above 1 per cent for at least 60 minutes in all trials. When all entrances were closed, CO levels were still above 1 percent after 24 hours. Levels were maintained after the engine was switched off.
In paper 3, Porton Down had another go, but their model told them that within a complicated sett system, the CO left dead spots. When they repeated Defra's number 2 'trial' - possibly with the same old Rangy (one would hope the taxpayer didn't fund two) they achieved similar results in all conditions of wind speed and soil porosity.

In paper 5 (2006) Defra had a blast with a portable generator - presumably the Rangy 3.5l automatic had eventually died. They had its portable replacement de-tuned to deliver levels of CO greater than its 4 wheeled predecessor and in a series of trials, all exceeded the target delivery of 1 percent concentration of CO for at least one hour.

In paper 8, Defra were looking at soil porosity and had mixed results until somone suggested they seal the entrance hole around the delivery pipe. When this was done, all trials revealed CO (Carbon monoxide) exceeding the 1 percent concentration on all models. In one test Miracle-Gro was used to mimic large soil particle size (2.36 - 2.80mm) and we had visions of an artic load.... However from the accompanying illustration, this experiment was done in a test tube, so enough for Defra's window box perhaps, rather than 'gardening leave'.

They tried GPR to map actual setts and see if CO worked underground as well as in the above ground tunnels sandcastles they'd built. But it failed to map and the two computer models were at logger heads. So Defra's conclusion of this work is more than interesting. As is its comparison with the Badger Trust statement we quoted above. In the overview paper published July 2008 which summarises all the work with CO done in 2005/2006, Defra say of the computer model log-jam:
"however by this stage of research two other viable culling techniques had been identified and further work on fumigation [with CO] had been suspended.
And this is the bit Trevor missed
"Although significant additional work would still be required to demonstrate the efficacy and humaneness of CO fumigation in the field (including regulatory approval) the most recent work suggests that development of a CDF model to predict gas flow within badger setts could be achievable. Defra July 2008"

If you have a spare three hours, all the papers can be seen here. Most indicate time pressure to deliver, and, as we've come to expect from the passengers on this miserable but highly beneficial gravy train, request 'more research' to confirm their findings.


Anonymous said...

The report referred to by Trevor was, I believe: "Further development and validation of a CFD model of gas diffusion within a soil tunnel, A report to Defra, 25 June 2008" available at http://tinyurl.com/5jzvop

This concludes on page 21 stating: "The conclusion based on the results obtained in Objective 3 and the subsequent
revised experimental design show that the current understanding of the physical
processes for the dispersion of CO in soil is insufficient for modelling the dispersion
of the gas. This may be due to the deviation of real soil from the assumption in the
CFD software that it is a uniform substrate.
Based on the findings it is recommended that no further work be carried out to
assess the use of the porosity model in Fluent to model transport of gas through soil."

Could you please give us the reference for what you refer to as "The bit Trevor missed"?

Matthew said...

Anon 10.01

Quotes are from the end and conclusion of p.2 of 2 which thumbnails all the rest of the work.