Sampling heads
In general terms we draw a known volume of air using a sampling pump through a suitable sampling medium. For particulates and fumes it would generally be a filter paper. A typical sampling train for personal monitoring would look like this with the sampler mounted in the breathing zone.
A personal sampling pump would be connected to a sampling head containing a suitable filter via a length of tubing. The pump is normally worn on the belt but it can be mounted on the back or the chest in a suitable harness. The sampling head, however, must be in the breathing zone for a valid sample. Dust is particles of solid material around 1µm to 1mm diameter. Larger particles are too heavy to remain airborne. Fumes are smaller than dust. They are solid particles formed by condensation from a gas and the particle size is typically <1µm. Dust can further be categorized into size fractions: Total Inhalable Dust, Respirable Dust and Thoracic dust. Here is a graph of the sampling convention.
Personal sampling heads
Many industrial and construction sites have the potential to expose their staff to harmful dust, vapours and gases. Inhalation is usually the most significant route of entry into the body and so monitoring the air they breathe is vitally important :
Total Inhalable Sampling Heads
Total inhalable sampling heads collect all fractions of particulates (up to 100µm) which enter the nose and mouth during breathing, i.e. everything that is available in the air to be breathed in. lt is possible to size select using some of the heads with the use of PUF ilters (see section 2.5) but if you are only interested in the Respirable Fraction it would be preferable to use a cyclone head.
I.O.M. Type Head & Cassette (P109009A & P109010)
The I.O.M. type inhalable dust sampler is the most commonly used head for Total Inhalable Dust sampling. Developed by the Institute of Occupational Medicine, this type of sampler is used with a cassette ensuring that no sample is lost on the walls of the sampler. The whole cassette including the filter paper is pre- and post-weighed ensuring that the entire sample is accounted for. The I.O.M. type head uses a 25mm filter housed in a cassette which is pre-weighed as a single unit. It is operated at a 2.0litre/min flow rate.The IOM type head has the advantage of being able to sample different size fractions simultaneously through the use of PUF filters. See Section 2.5 for description of its use with PUF filters. The diagram below shows the component parts:
The l.O.M. Type Head
Conical Inhalable Sampler
The Conical Inhalable Sampler (C.I.S.) is primarily used when there is a need to sample a high concentration of particulate. A larger size of filter is therefore used (37mm). The cone is designed to spread the sampled dust evenly over the filter which is housed in a cassette. The cassette, complete with 37mm filter is pre-weighed as a single unit. The C.I.S. head is operated at a flow rate of 3.5l/min.
Higgins-Dewell Sampling head
Higgins-Dewell Sampling Head (11600B) The Higgins-Dewell (HD) cyclone is most commonly used in Europe and is usually made from conductive plastic, although metal versions are available.The cyclone head uses a 25mm filter cassette which can we weighed complete. 37mm heads are also available. The cyclone best operates at 2.2l/min. The diagram below shows the component parts.
Additional information
| Air quality general |
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