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Understanding Composite Meth Testing

Updated: Oct 14, 2018

What is a composite Meth Test?

When we test a property for Meth or ‘P’ we take a swab of a wall or surface in a 10cm by 10cm stencil – this is the sample or patch. Each individual sample is known as a discrete sample. A discrete sample can be analysed by itself or added to other samples to make a composite sample.

The two main labs, Hills Laboratories and Analytica Lab, both offer two types of Composite Lab tests. Lab Composite and Field Composite tests. MethTec only offers the Lab Composite option.




Lab Composite Test

For Lab Composite we take either 5 or 10 Discrete Samples. These are coded Individually so that each patch tested can be traced per room and per wall and then sent off to the Lab. They could be tested individually for individual results but we get the Lab to combine the samples together and to test it in a composite test. Why do a composite test? Costs, but more on that later.

A Lab Composite Test is analysed by the Lab and we get a numerical figure as to the level of contamination. A Negative or Non-detected result is shown as a Sample Composite <0.02 with a Theoretical Maximum of <0.1 Micrograms per 100 sqcm. A reading of Meth Contamination is taken as a microgram per 100 sqcm 100 sqcm being the 10cm by 10cm stencil) or read as µg per 100 sqcm. A positive or detected result will give an average as the Sample Composite, in the example we are using the Sample Composite is 6.81 µg per 100 sqcm giving a Theoretical Maximum of 68.09 micrograms - allowing for rounding that is 10 x 6.81 (10 being the number of samples taken).

A result of 6.81 µg per 100 sqcm is a Positive result meaning Meth has been detected in at least one of the samples taken. A level of 6.81 µg per 100 sqcm is Above the NZS8510:2017 Standard of 1.5 µg. In this case you need to get each sample tested individually to establish the contamination level in each room sampled.

With us having done a Lab Composite test the Lab holds our Discrete Samples for 2 weeks so we can now get them to test the Individual Samples – at this point we may not need to go back to your property to retest.

In this case we would suggest that you contact your Insurance company however they are unlikely to decontaminate your property.



Discrete Sample Testing

As the above Lab Composite test came back at 6.81 µg and a Theoretical Maximum of 68.09 µg we individually tested each sample. This is done to get a level of contamination for each sample/room tested. A room testing under 1.5 µg doesn’t need to be Decontaminated under the NZS8510 Standard – however you may well decide that you still want to decontaminate the room.

The Results were:

Lounge 0.95 µg

Kitchen 2.95 µg

Dining 1.02 µg

Bedroom 1 0.20 µg

Toilet 40.66 µg

Bathroom 9.36 µg

Bedroom 2 5.23 µg

Bedroom 3 0.85 µg

Garage 4.51 µg

Bedroom 2* 0.44 µg

Total 66.17 µg

The combined value of the Discrete Samples, 66.17, is in line with the Theoretical Maximum level of the Lab Composite, 68.09 µg.


Field Composite Testing

A Field Composite test is where up to 5 discrete samples (individual samples) are taken and added together in one vile to be tested as a group. As they are all put into one vile that can't then be tested individually.


We don't advertise a Field Composite option. We think that as Discrete (Individual) Samples are taken and then combined at the Lab for a Lab Composite this gives the ability to retest the Individual Samples should the initial Lab Composite test come back positive. This saves time and money for the customer.

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Part 1 of a 2 Part Story on Meth

This is worth a watch. Paddy is doing some good work here https://www.newshub.co.nz/home/new-zealand/2020/07/the-sad-reality-of-how-meth-is-tearing-new-zealand-families-apart.html We will post Part 2

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