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Asbestos Air Monitoring - NOHSC 3003: (2005)

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Queensland and NSW Laboratories are an Australian Occupational Hygiene & Environmental Consulting firm, specialising in the management and assessment of asbestos containing materials (ACM). Their team of AQIS certified and NATA Accredited occupational hygienists provide Air Monitoring services for asbestos Australia wide and also in the Asia Pacific and Indian Ocean regions.        

General Method Description - NOHSC 3003: (2005) Asbestos Air Monitoring  

A sample is collected by drawing a measured quantity of air through a membrane filter by means of a sampling pump. The filter is later transformed from an opaque membrane into a transparent, optically homogeneous specimen.  The respirable fibres are then sized and counted in accordance with defined geometric criteria, using a phase contrast microscope and calibrated eyepiece graticule. The result is expressed as fibres per millilitre of air, calculated from the number of fibres observed on a known area of the filter and the volume of air sampled.  

Exposure Monitoring For Occupational Situations  

Exposure monitoring involves the taking of regular samples within the breathing zone to determine a person's risk from, or level of exposure to, airborne asbestos fibres. This method is intended to be used for the sampling of airborne asbestos fibres in occupational environments where the airborne fibres are known to be predominantly asbestos.  This  method shall be used to determine compliance with the exposure standard for asbestos processes.  This includes maintenance, construction and demolition work directly concerned with in situ asbestos containing materials (ACM), or working with chrysotile as permitted under the exemptions from the chrysotile ban brought into force nationally in December 2003.  

Strategy for Exposure Monitoring  

Exposure monitoring is carried out to achieve one or both of two major objectives:  

• To assess exposure relative to the exposure standard.
• To provide estimates of exposure for epidemiological investigations of morbidity and mortality, and for civil or worker's compensation legal reasons.  

Sampling procedures should be arranged so as to cause minimal interference with the work activities.  All sampling must be conducted in the breathing zone of a worker so that the results are indicative of the worker's exposure to asbestos fibres under representative working conditions.  

Total Sample Duration and Number of Samples  

Sample duration is influenced primarily by the reason for monitoring, the level of fibre concentration to be measured, the concentration of non-fibrous dust and the requirements of the analytical method.  This may result in more than one single sample being required.  The total sample duration should aim at collecting a sample that is representative of the period in question, usually an entire shift. 

Detailed knowledge of work being conducted is necessary at all times, especially when the actual asbestos work does not cover the entire shift.   Control Monitoring For Other Situations  

Control monitoring uses static samples to measure the level of airborne asbestos fibres in an area and is designed to assist in assessing the effectiveness of implemented control measures. This method is intended to be used for the control monitoring of airborne asbestos fibres in situations that include sampling in the following situations:  

• Outside asbestos removal and encapsulating areas.
• At the clean end of asbestos decontamination units.
• For clearance sampling after asbestos removal and encapsulating.
• Inside buildings, structures or ships which contain asbestos.  

This type of sampling is often conducted in areas that contain high proportions of non- asbestos fibres or particles, which conform with the geometric requirements of a fibre as defined by this method. Many experienced occupational hygienists recommend against this form of control monitoring as these non-asbestos fibres cause problems in interpretation, especially where the results of the monitoring are intended for use in estimating risks to health from suspected environmental contamination by airborne asbestos fibres.  In such situations it is inappropriate to consider that the results from such monitoring have the same significance in terms of health consequences as does exposure monitoring outlined in Part 6.  

Strategy for Control Monitoring  

All sampling must be conducted so that the results are representative of the particular and specific situation being monitored.  Generally, only static sampling is used, and this should be taken over a single sample duration of not less than one hour. In situations where asbestos is actively being removed or disturbed, dust concentrations may vary widely both within a single day and from day to day, or from place to place.  Additionally, variations in work procedures produce concentrations, which can vary over one or more orders of magnitude.  These factors may influence airborne levels obtained outside the asbestos removal area.  

Air sampling outside asbestos removal enclosures is often carried out to ensure that negligible airborne asbestos fibres are present.  However, some results can be misleading due to non-asbestos fibres, which monitoring will detect but not identify by the MFM.  Air sampling can be used for testing the reliability of enclosures when they are initially installed.  Once it has been established that such enclosures are controlling dust emissions, the emphasis should be placed on more efficient methods of measuring control, such as daily checking of the integrity of the barrier, negative pressure conditions, and the work practices that are carried out inside the enclosure. 

The choice of sampling conditions and interpretation of results should be determined by an experienced occupational hygienist.  

Various State authorities and occupational hygienists use action levels that require review and/or revision of risk control measures.  These levels have previously been estimated by paraoccupational sampling, which is now known as control monitoring. Air sampling in an environment which is representative of normal work activities is desirable, however the artificial generation of an unrealistic environment is not acceptable.  The use of air sampling which is associated with the deliberate creation of artificial contamination by sweeping, beating, or the blowing of air on to asbestos containing materials or contaminated areas (that is, `aggressive' air sampling) must not be employed.  Data obtained under such conditions do not reflect current or future activities and therefore are of no value in the assessment of risk.  Furthermore the practice may result in the transference of contamination from one part of a building to another without significantly affecting the measured airborne asbestos fibre concentration and/or can lead to misleading results due to the disturbance of non-asbestos fibres in the environment.  

It is important to understand that air sampling should not be used as a substitute for frequent and thorough inspections by an occupational hygienist experienced in asbestos matters.  Careful visual examination will reveal situations that are likely to create future contamination problems.  Meticulous cleaning, resulting in the absence of any visible dust, will generally reduce contamination levels to below detectable levels.

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