Asbestos fibres

Brunel ABS320 for phase contrast fibre counting.

The microscopy requirements for the identification and particle counting of asbestos are exacting, and are covered by the Health and Safety Guidance (HSG) 248 Appendices 1 and 2 of the Health and Safety Executive (HSE). www.hse.gov.uk/asbestos/index.htm is an excellent resource for up to date information and further references.

Asbestos fibre counting by phase contrast microscopy has very specific requirements, and there are relatively few microscopes that can meet the phase contrast optical performance criteria. This is measured with a Phase Contrast Test Slide that was developed by the Health and Safety Laboratory (HSL) on behalf of the HSE and in collaboration with ULO Optics (formerly PTR Optics) and the National Physical Laboratory (NPL). The slide is known as HSE/NPL Test Slide, and its purpose is to provide a reproducible phase object to check the suitability of microscope phase systems for asbestos fibre counting. The test slide has 7 bands of 20 lines each, and the width of the lines in each band decreases. The master engraving was produced by the NPL using a ruling engine, and each of the HSE standard test slides is an epoxy replica of the NPL master. HSL certifies the test slides as satisfactory for use to set up phase contrast microscopes and categorises them into two groups

1. Those that have band 4 lines fully visible and band 5 partially visible - these are given red documentation

2. Those that have band 5 fully visible and band 6 partially visible - these are given green documentation.

Any suitable microscope must be able to resolve either band 4 on a red label slide (with maybe parts of band 5 visible) or band 5 on a green label test slide (with maybe parts of band 6 visible). The x40 phase objective with a x12.5 eyepiece with a Walton and Beckett graticule is the required combination.

The Brunel ABS320 meets the green label standard using test slide 6609 certificated and confirmed by the HSL themselves. We believe that it is the lowest price microscope on the market to do so. The use of the test slide is required by the HSE to ensure microscopes are properly adjusted when testing for compliance with the UK asbestos control limits. These are robust industrial microscopes finished to a very high standard and with a very modern design. The light source is a Kohler LED unit integral to the base of the microscope. This makes the microscope an ideal instrument for phase contrast applications, and the trinocular ABS320 is, we believe, the lowest priced phase contrast microscope that meets the HSE specification for asbestos fibre counting that is currently available.

A particular feature is the large rectangular mechanical stage with drop down co-axial controls. The ABS320 is specifically configured to provide the optical specifications needed for asbestos fibre counting. This consists of infinity corrected x10, x20 and x40 plan brightfield phase contrast objectives together with an easy to operate slider phase ring system in the condenser. This allows an easy change ‘toggle’ movement from x10 to x40 phase contrast presentation. For those who may want a full magnification range in phase contrast, a Zernicke phase condenser and further phase contrast objectives are available as accessories. x12.5 eyepieces, one with a focusing Walton and Beckett graticule, green interference filter and a centring phase telescope complete the specification.

The co-axial coarse and fine focus controls have a graduation reading in 2 microns. The total focus range covers 35mm and the movement runs in extra wide precision ball-bearing hardened steel tracks. Tension adjustment and safety auto focus stop units are fitted as standard.

The specific feature of the Brunel ABS320 series is the potential flexibility, both in optical performance and image capture systems. We believe that at this budget there is no other microscope that can offer this flexibility and excellent results with phase contrast microscopy, together with green certification for asbestos fibre counting. There is an excellent carrying case with suitcase style handle and wheels which makes the ABS320 truly portable.

Price ABS320 Trinocular microscope - £1920.83 + vat complete for fibre counting

Price ABS320 Carrying Case - £179.17 + vat