In order to avoid false positives, ALERT runs a algorithmic statistical analysis.
It must see a statistically significant number of fibres rotate within a sample set of at least 30 fibres (a minimum of seven must rotate) to give a Warning.
After a second sample set has been tested and passed the test, ALERT will Alarm with a statistical confidence level of 99% that asbestos is present in the sample.
When a set number of fibres have been detected, a statistical analysis is completed to determine the amount of rotating fibres out of that sample.
ALERT will NOT alarm on one single rotating fibre.
The unit can see up to 600 particles per second and as this "soup" of particles pass through the lasers, it is possible they may bump each other inadvertently changing the angle of non-asbestos fibres in the sample. It is therefore possible that some non-asbestos fibres may rotate.
Algorithmic statistical analysis achieves 99% confidence level
European Patent Number
Almost uniquely among fibrous materials, asbestos has a magnetic susceptibility that results in a magnetic torque when the material is in the presence of a magnetic field - which means the asbestos fibre will rotate and try to align with the magnetic field.
When ALERT identifies it has seen a fibre (based on the peak to mean ratio of its scattering pattern) ALERT will record the angle (or orientation) of that fibre as it passes through the first laser in the optical chamber.
The sample is then passed through a strong magnetic field and a second laser.
Due to the unusual paramagnetic properties of asbestos minerals (which contain magnesium and / or iron) the asbestos fibres (of all types) will rotate.
The extent to which the fibres have rotated whilst passing through the magnetic field.is measured by second laser.
The system can see up to 600 particles per second and pairs the fibres passing through the system in nanoseconds based on the time in takes to transition between the two lasers (the inter-arrival time).
Paramagnetism of asbestos
A peak to mean ratio test is the performed on the scattering patterns which enables us to distinguish fibres from other non-fibrous particles.
FIBRES present a single dominant peak with a high peak to mean ration, differing markedly from other airborne particles present. (left hand image)
DROPLETS display a scattering pattern of concentric rings which is reflected in the symmetry of the multiple peaks. (middle image)
PARTICLES such as irregular dust particles produces no distinct peaks or symmetry. (right hand image)
Note: WHO Respirable Fibres
ALERT does not characterise fibres by the same specifications as the World Health Organization (WHO). Their definition of a respirable fibre = a diameter of less than three micrometres and a length of greater than five micrometres; and a length to width ratio of greater than 3:1.
It is important to note, that ALERT units can and do detect fibres that fall within WHO's size definition but it uses the peak to mean ratio described here to distinguish a fibre.
Using a pump, ALERT draws a controlled air sample through it's optical chamber pulling all particles and fibres in the sample through a laser beam.
The laser shines through every particle and fibre creating a scattering pattern individual to each particle and fibre type.
Light scattering technology
The process ...
Patented, world first technology
The ALERT devices provide a method of rapidly detecting airborne asbestos with an alarm being triggered when a 99% statistical confidence in the presence of asbestos is reached.
The technology is based on the analysis of spatial light scattering patterns from individual airborne particles and the utilisation of a magnetic field to determine the presence of asbestos.
Light scattering technology distinguishes fibres from particles
Paramagnetic properties of asbestos fibres distinguishes them from non-asbestos fibres
Complex algorithmic statistical analysis achieves 99% confidence level