Particle size Elements of a sampling system

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6.3 Sampling Records

Full details of the sampling performed should be recorded and retained. The record should indicate when the monitoring was done, who and where was monitored, details of the equipment used, the operations in progress at the time of the survey and the results obtained. In most countries records of monitoring should be available to employees or their representatives.

6.4 Sampling for Airborne Particulates

6.4.1 Particle size

Most industrial aerosols contain particles of a wide range of sizes. Source: Adrian Hirst Figure 6.1 - Particle Sizes 64 The behaviour, deposition and fate of any particular particle after entry into the respiratory system and the bodys response depends on the nature e.g. solubility and size of the particle. In general there are two size fractions of interest to occupational hygienists and these are termed total inhalable and respirable. Total inhalable dust is the fraction of airborne material which enters the nose and mouth during breathing and is therefore liable to deposition anywhere in the respiratory tract. The particle sizes of total inhalable dust are up to 100 microns. Respirable dust is that fraction that penetrates to the deep lung where gas exchange takes place. The particle sizes of respirable dust are up to 10 microns. It is important to appreciate that particle behaviour is dependant on factors such as particle shape and density, wind speed and direction, breathing rate and whether breathing is by the nose or mouth. In practice the number and mass of particles of 50 microns in a typical airborne dust cloud is small.

6.4.2 Elements of a sampling system

When performing personal monitoring for airborne particulates there are three main sampling system components which go up to make the “Sampling train”. These are the Pump, Filter and Sampling Head. The pump is used to draw air into the sampling head and collect any particulates on to a filter. 65 Source: SKC Limited Figure 6.2 – Elements of a Sampling System The pump is a battery powered device which is worn by the worker. The pump should be able of operating at a constant flow rate typically between 1 and 2.5 litres per minute for prolonged periods of up to 8 hours. The calibration of the pump as well as the measurement of the sampling time allows us to calculate the volume of air which is being sampled. The filters need to be capable of collecting all of the particulate material which is brought into them and at the same time need to be compatible with any subsequent analysis technique. Typically these are glass fibre filters and membranes filters. When the analysis is for dust then a glass fibre filter is used. The filters are weighed both before and after use so that a weight change can be determined. This change in weight can be used with the flow rate and sampling time to arrive at a measured exposure using the equation below. 66 Concentration mgm3 = Weight gain mg x 1000 Flow rate litremin x Time min Explanatory note – the figure of 1000 is needed in the numerator of this formula in order to convert the sample volume in the denominator from litres to m3. The above formula can also be expressed as : Concentration mgm3 = Weight gain g Flow rate litremin x Time min where the weight gain is expressed in the units micrograms g. The sampling head allows the filter to be held in the correct position but can also act as a size separator. Total inhalable dust is typically measured using the IOM sampling head although other devices are also available. Respirable dust is measured using a cyclone pre-selector which removes the larger particles before they reach the filter. Source SKC Limited Figure 6.3 - IOM Inhalable dust sampling head left and cyclone respirable dust sampling head right 67

6.5 Sampling for gases and vapours