Sampling Techniques Types of Sampling

59 Not surprisingly different sampling techniques are needed for each of the above states of matter.

6.1.1 Sampling Techniques

The fundamental requirement of any measurement technique is that it should be appropriate for the purpose of the measurement. This means it should provide information necessary for the decisions which will be made on the basis of that information. „Monitoring‟ or “Sampling” means the use of valid and suitable occupational hygiene techniques to derive a quantitative estimate of the exposure of employees to substances hazardous to health. Only validated monitoring methods should be used, these are published by organisations such as the HSE in the UK and NIOSH in the USA. Other countries also produce methods and in some cases these are specified as being compulsory within local legislation. In the case of airborne contaminants monitoring involves the periodic or continuous sampling of the atmosphere at the workplace and will usually require sampling in the breathing zone of the operative by means of personal sampling equipment. In addition to personal monitoring, fixed positionstatic monitoring can also offer limited information as to an individual‟s exposure. However, it can provide a guide to the sources of contaminants, effectiveness of control measures and the general workroom atmospheric concentrations.

6.1.2 Types of Sampling

There are five main types of sampling: Grab Grab or snap sampling can be used as a screening technique; it will give the concentration of a contaminant at a specific time and location and will help to confirm the presence of andor identify a suspected contaminant. 60 C o n c e n tr a ti o n Time Source: Adrian Hirst Short term Short term monitoring will determine concentrations over a short time period, normally up to 10 or 15 minutes. Results are normally calculated as a time- weighted average TWA and can be compared with any relevant recommended short term exposure limits especially WELs and to quantify exposures to acute hazards e.g. cadmium. C o n ce n tr a ti o n Time Source: Adrian Hirst Long term Long term monitoring is similarly determined on a time-weighted average basis and related to long term 8 hour TWA recommended limits. Half Shift 4 hours, or the time to complete a specific operation or full shift nominally 8 hours and normally the time periods monitored. 61 C o n ce n tr a ti o n Time Source: Adrian Hirst Continuous Monitoring will indicate the variations in concentrations and is similar to grab sampling in that peak levels can be identified as well as the average concentrationsexposures being determined. C o n c e n tr a ti o n Time Source: Adrian Hirst Bulk In some circumstances, bulk samples of the substances being handled may also be taken and analysed for identification purposes, but it is not possible to relate the results from bulk samples to the airborne samples collected. However, with some contaminants, such as asbestos, bulk sampling is an essential part of the identification process. 62 The sampling types described above and the exposure limits quoted in EH4O in the UK or other legislationdirectives are based on the assumption that inhalation is the main route of entry into the body. However, skin absorption and ingestion can also occur and the only sure way of measuring exposure to substances entering the body by these routes is to apply biological monitoring methods. Usually, such methods measure the amount of a substance or of one or more of its metabolites in one or other of the two accessible body fluids – blood or urine. Details of such sampling techniques will be covered in Section 8 of this course manual. Measurements for particular substances at a particular time tell only part of the story, and it should be remembered that concentration can vary as process changes etc, occur. Proper sampling strategies must be adopted to decide which groups of workers, which plant locations and which shifts should be monitored. One of the first questions you should ask about of any sampling technique is what will the results tell me. What are the norms against which they may be judged?

6.2 Sampling Equipment