TESTING ASBESTOS

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Asbestos Sampling and Analysis

 

Site specific testing strategies are formulated to meet the requirements of each asbestos sampling  project.

 

Our trained asbestos surveyors carry out asbestos sampling of suspect material in accordance with HSE Guidance Note HSG 248, MDHS 100 and in-house procedures.

 

Accredited Asbestos Sampling Service

 

The asbestos sampling carried out is then analysed by an ISO 17025 accredited laboratory in accordance with HSG 248 and in-house procedures using polarised light microscopy.  

 

Example of asbestos sampling equipment 

 

• Set of screwdrivers

•  Chisels

•  Pliers (smooth jaws or jaws filed flat

•  Pincers

•  Set of core samplers or cork borers

•  Stanley type knife with spare blades

•  Cloth backed tape

•  Foil Tape

•  Polyfiller or other type of filler

•  Wet wipes

•  Self seal sample bags

•  Sample point labels

•  Warning signs

•  Polythene sheeting

•  Type H vacuum

•  Torch

•  Camera

•  Ladder and/or work platform

•  Appropriately labeled waste bags for overalls, cleaning cloths, disposable RPE, etc.

•  A labels

 

This is not an exhaustive list and other items that we would use are:

 

•  Binoculars

•  Inspection mirror

•  Hammer, Pinch Bar, Pad Saw, etc (Type 3 surveys)

 

Protective equipment used:

 

•  RPE to meet the assessment: usually disposable with FFP3 filtaration or orinasal with P3 filter

•  Type 5 disposable coveralls

•  Suitable footwear, i.e. Wellington boots, disposable overshoes, etc.

•  Disposable gloves

 

Asbestos Sampling Methods

 

All methods selected must take account of the duty to minimise exposure. Regulation 16 requires that the employer prevents the spread of asbestos or, where this is not reasonably practicable, reduces it to the lowest level reasonably practicable. There is also a possibility of spread of asbestos if surveyors do not

 

a)   select appropriate work methods;

b)   seal the sample site;

c)   thoroughly clean their equipment and/or containers used for equipment or waste, and

d)   thoroughly clean any dust and debris that they may have generated during their work.

 

Methods that produce the best results for asbestos sampling are similar to those used by our asbestos removal division including controlled wetting (by injection or airless spray as appropriate) and shadow vacuming. Surrounding most of the sample by the plastic sample bag is also an effective way to contain dust and debris.

 

Wherever feasible the plastic self seal sample bag will be taped directly below the sample spot so that should there be any spillage, it will be collected into the bag. Wherever practicable, a sheet of plastic of at least a square metre (drop sheet) will also be placed below the sampling point: should there be any accidental spillage, this will aid cleaning the area since it can be wetted, rolled up and double bagged as asbestos waste. A drop sheet is essential to protect soft furnishing such as carpet. Howether, the placing of the drop sheet should not introduce any slip or trip hazards.

 

Asbestos Sampling Technique - Sprayed Coating and Loose Fill

 

Although MDHS 100 recommends a general sample size of 3-5cm, the taking of such large samples is not recommended with such friable material. In addition, the asbestos content of sprays and loose fill is high and they are homogeneous in composition. Hence a large sample is not required for analysis. On rare occasions a spray is two layered with a decorative spray overlaying a fireproofing or acoustic spray. Decorative sprays are usually denser in appearance because of the carbonate or similar filler used to whiten them and they are chrysotile based. They are usually only several mm thick and as such can be formed into relatively crisp edges. Inspection will usually show if the decorative spray overlays another spray coating as there will be no sharp corners.

 

Un-encapsulated spray coating and loose fill: The most appropriate method is to use tweezers or similar to lift a small piece of loose debris which will be present for most installations. If no such debris is found, then a small piece can be lifted from the surface.

 

Shadow vacuuming can assist providing that:

 

a)   the hose of the vacuum cleaner will extend that far;

b)   there is sufficient safe access for the two people required for the task;c)   the equipment is used so that the sample can be transfered to the sample bag.

 

Wetting by airless spray can be effective but the spray must not point at the dry installations or there will be considerable fibre release: it should mist across the surface. No making good is needed on completion of sampling.

 

When sampling encapsulated spray, rather than break into an encapsulant, it is generally more efficient to spend time looking for areas of debris, overspray or incomplete asbestos encapsulation. If no such debris can be found, wetting by injection is the most effective method to control fibre release. Shadow vacuuming, if reasonably practicable, can also assist. The surface should be cut in a T with a sharp knife so that a small piece can be lifted with tweezers. The sample area will be made good afterwoods.

 

Asbestos Sampling Technique - Thermal Insulation

 

A core sample of about 2.5 cm should be taken from surface to base, i.e. from outside of the insulation to the pipe surface. Large sample sizes are required so that small quantities of asbestos will not be missed in insulation that was not evenly mixed on site. Older insulation was often applied as more than one layer. It was also often patched (e.g. when the system was extended; valves inserted or repairs were made to the insulation) and the old asbestos insulation could be mixed in with the later asbestos free during patching.

 

Asbestos thermal insulation came as either pre-formed sections or plastic which was mixed with water on site and applied by trowel onto the surface being insulated. The most usual of both types was either 85% magnesia (15% asbestos of any type) or calcium sillicate which was developed later. Many installations were coated by a hard-setting material (also containing asbestos) which was smoothed and painted. Bulldog was developed as a hard waterproof covering for outdoor insulation but was considerably higher asbestos concentrations were made, including Caposite (more than 85% amosite bound with sodium silicate) which was usually held onto pipes with a calico wrap. This is a high release, homogeneous product and small sample sizes similar to those taken for sprays and loose-fill are recommended for this product.

 

Asbestos Sampling Technique - Asbestos Insulation Board

 

Wetting can only occur through spray wetting of unsealed/unpainted surfaces and hence asbestos sampling from already damaged areas is advocated so far as is reasonably practicable. Shadow vacuuming is also recommended provided that if the material is at high level, there is sufficient safe access for the two people required and the H vacuum cleaner hose will reach the sample point. If the material appears to be the typical Asbestolux type, small fragments of damage measuring a few cubic mm can be sufficient to detect the amosite which is present in significant concentrations. Larger samples, at least 2.5 cm2 in surface area, should be taken of other materials, particularly if there may be a need to determine whether the material is asbestos cement or asbestos insulating board. Samples are usually taken with pliers (with ridged grip either ground off or protected to avoid cross contamination) or pincers, all preferably using scribe and break.

 

Asbestos Sampling Technique - Ropes, textiles and paper

 

These materials are generally made with high concentrations of crysotile which can be readily wetted by airless spraying, ensuring the spray is initially applied as a "mist" and not pointed directly at the material. If they are made from crocidolite (recognisable from colour in nearly all cases) extra care must be taken to ensure sufficient wetting. Amosite is rarely encountered in such products. A few strands of the material cut with a sharp knife is sufficient to establish the fibre type of most woven materials although care should be taken with ropes as some of older manufacture contained a different asbestos type in the core. Great care should be taken not to flex the material during sampling as such movement can release fibre from more distant un-wetted areas (e.g. during sampling of woven chrysotile blankets hung as fire barriers above false ceilings).

 

Asbestos Sampling Technique - Asbestos Cement

 

Only the surface of asbestos cement is wetted by spray application. Samples should be at least  3 cm2 to ensure detection of any low concentrations of amphiboles that may have mixed with the predominant chrysotile and to allow for water absorption testing for differentiating between asbestos cement and asbestos insulating board. The sample is usually snapped off using pliers or blunt nosed pliers. Sharp nosed pliers should be avoided as a crack can propagate from the tip. The greatest hazards of sampling asbestos cement are possible falls through fragile roof sheets or cracking of the material which can allow rain to enter through roofs or allow flue gases to escape.

 

Asbestos Sampling Technique - Textured Coating and Decorative Plasters

 

Effective wetting for sampling is not possible. These low fibre release materials but shadow vacuuming should be used where practicable. The material is generally scraped /levered away with a chisel or similar sharp tool. Where it has been applied over plasterboard it is usually reasonably easy to detach a sample. Howether, material that has been thickly applied to some substrates (e.g. concrete) can be more difficult to remove and may involve both hammer and chisel. A sample size of at least 5 cm2 is required for a thickness of about 5 mm since the material contains only low concentrations of very short and very fine chrysotile that is generally not really visible during analysis. Thinner samples require proportionately larger samples.

 

Asbestos Sampling Techniques - Other low fibre release materials

 

Many other materials are most readilly sampled with a knife to either cut (e.g. bituminous materials) or scrape (e.g. reinforced plastics and resins) the sample from position. Care should be taken if shadow vacuuming is employed in conjunction with scraping as the sample can be easily lost in the suction. The greatest hazard is that removal of the material will alter the integrity (e.g. roofing material, gaskets).

 

 

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