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Is Fumigation Effective? You only need to know one thing.

Friday 18th November 2022

How do you know a fumigation has been effective?

My mentor, Mike Kelly, had a saying:

“If you’re not measuring, you’re not fumigating.”

I think he might have stolen the phrase from the great Bishu Chakrabarti who in turn nicked it from Jan van Someren Graver but, for our purposes let’s just take it as an undisputable axiom from three of the world’s greatest ever authorities on fumigation.

We measure using optical interferometers, our weapon of choice, which gives us exact readings of gas concentration inside whatever we are fumigating. But why is measuring so important?

I need to take you back in history, to an incredible chemist who is much reviled by the history books.

Fritz Haber, great scientist, unfairly characterised as a historical villain

Fritz Haber had a rule and it looks like this:


K is a constant here. Basically Haber’s Rule means that temperature and concentration are inextricably linked. If you increase one, you can get the same constant by decreasing the other by the same factor and vice versa.

The constant that fumigators are interested in is the moment when time is long enough and concentration is high enough to kill whatever insect is infesting our food/building/plane etc. We call it the CTP because it’s as simple as multiplying concentration and time (Concentration Time Product).

Concentration Time Product (CTP):

The dosage of a fumigant required to kill an insect is a relationship between the dosage (concentration, C) applied and the time (in-hours, T) to which the insect is exposed.

It is expressed in gram hours per cubic metre (g.h/m3).

So, CTP in g.h/m3 is the concentration in g/m3 of the fumigant applied multiplied by the exposure time in hours.

For example, if an average concentration of 32g/m3 is maintained over a 24-hour period the CTP is 32 x 24 = 768 g.h/m3.

There are a range of CTPs for different insects and different gases. We are always sure we have reached the CTP for any fumigation that we do. The sad thing is, however, pretty much every fumigation company out there don’t even measure gas concentrations! They add the right dosage and assume everything is going fine.

The problem with this is the familiar problem of genetic resistance to fumigants. Fumigation have been done so badly for so long (globally) that insects have become resistant to many of the common fumigants.

Luckily, we have apparatus to test resistance and techniques to overcome it. But it takes a fair amount of experience and knowledge to get it right.

Next time you have a fumigation, ask the fumigator what CTP they are aiming for. If they can’t answer, click the ‘get in touch’ button below.

Effective fumigation measuring fumigants insect control by fumigation
Getting into fumigation can lead to all sorts of specialised apparatus being employed

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