Asbestos tests

There are basically two types of asbestos test; the air test and bulk sample analysis. The first tests for the presence of asbestos fibres in the air and the second for the presence of fibres in a material.

Bulk sampling test

This test is used to analysis a sample of a material for the presence. You can find more details on the asbestos analysis page.

Air test

As you can imagine, counting fibres a 100th of the width of a hair can be quite challenging but believe it, or not, it can be done. The first stage of an air test is to collect a sample of fibres in the air. This is achieved using a specialised air pump which sucks air through a filter. The flow of the air through the filter is measured (using a flowmeter) to ensure that its consistent because by multiplying the flow by the time the pump is run its possible to calculate the amount of air (in litres) that has been sampled.

For example, if the flow is 1cm3 a second its easy to calculate that 60cm3 of air has been sucked through the filter in a minute. In a typical test two pumps will be run, one for 10 minutes at a flowrate of 4 litres per minute (40 litre in total) and one for 4 hours at 1 litre per minute (240 litres). The 4 hour pumps may be doubled up in case one fails. In large rooms multiple pumps may be necessary.

Once the sampling is completed the filters are analysed under a microscope. The filter area is divided into 100 micrometer squares and the analyst picks 100 squares at random and counts the fibres he find in each square. Abestos fibres are known to be greater than 5 micrometers in length and less than 3 micrometers in width (with a length to width ratio greater than 3:1). Any fibres within  this range are counted. This is significant because there are non-asbestos fibres which fall into this range. For the purpose of this test these are counted too, so its not always possible to get an entirely accurate result. 

Once we know the number of fibres in 100 squares we can calculate an average for the whole filter. i.e if we know there are 50 fibres in 100 squares and the filter has a surface area of 1000 squares we can calculate that there are approximately 500 fibres on the filter.

Finally, we know how much air we've sampled and we know how many fibres we've collected so the last thing to do is to calculate how many fibres are present in each mililitre of air. It is this figure (fibres per mililitre - f/ml) that is used to determine whether fibre concentration are acceptable for human occupation.

The control limits are as follows;

Chrysotile

0.3 f/ml for a 4 hour pump

0.9 f/ml for a 10 minute pump

Other asbestos (or unknown)

0.2 f/ml for a 4 hour pump

0.6 f/ml for a 10 minute pump.

This test is normally run after asbestos removal has taken place to esnure that the are is fit for re-occupation. However, home users may want to use it to determine whether an asbestos product has cotaminated their home.

You can find a list of asbestos analysts on the UKAS website. You are looking for family 'asbestos' and test 'fibre counting'.