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A breath of fresh air: PWE takes a look at a new technology that simplifies supplied air testing methods.

Checking the quality of supplied breathing air has, historically, been a time-consuming and expensive task. Today, however, with the advent of new air monitoring technology, the tests can be carried out quickly and easily, with the results being both immediate and cost effective.

In accordance with BS4275, BS EN12021 and the Control of Substances Hazardous to Health (CoSHH) Regulations, supplied breathing air should be tested at least once a month for carbon monoxide, carbon dioxide, water vapour, oil and oxygen levels. In the case of mobile breathing compressors, they should be tested each time they are used in a new location or if circumstances change (See Table A).

For those industries that are reliant on supplied breathing air, the need to check air quality is not only essential under these regulations but it is also vital to health and safety. Widely used throughout the petrochemical, nuclear and pharmaceutical industries, for example, supplied breathing air is also found in other industrial environments with large finishing departments such as in vehicle refinishing applications.

Mass Spectrometry

Requiring a significant financial investment, mass spectrometers are calibrated when installed and cannot be moved. Sensitive and bulky but chemically clean, they provide accurate test results of static samples. They also have one other drawback--they do not test at the flow rate required by breathing air.

Laboratory Analysis

Once an air sample has been taken, it can be posted to an external laboratory for remote analysis. Costing around 80 [pounds sterling] per sample, plus set up costs, this may appear to be relatively inexpensive but, in some applications such as petrochemical for instance, tests are required on a weekly basis. In addition, there is the time delay to be considered--it can take up to a week before the results are known. This has obvious implications for mobile equipment, as it must not be used until certified. A failure of any system must result in immediate prohibition of use and this cannot happen where there is a delay in achieving the result of a test.

Modern Tube Test Technology

Until recently, although it has been possible to obtain credible test results, on site, with tube technology, this has involved a stop watch and flow kit and has required the completion of individual tests on each substance. This could take well over an hour. With the advent of new technology and the launch of the F3000 from Factair, however, this timeframe can be reduced to less than 20 minutes.

Combining chemical reagent DraegerTubes with fourth generation instrument technology from Factair, the F3000 Safe-Air Tester provides an instant result for each contaminant, simultaneously. Designed for accuracy and ease of use, it enables regular checks of the flow and purity of compressed air breathing systems to be made with speed, reliability and consistency. With annual calibration costs of just 210 [pounds sterling] and tubes costing 14.02 [pounds sterling] per test, this new system is also very cost effective in use. Requiring a 5-minute purge and an average 13-minute test, it can give a reading in less than half an hour and, with basic training, will provide credible, certifiable results.

Specific to the hazards that are likely to be found in supplied breathing air as a result of a malfunctioning compressor, the F3000 is designed to simultaneously test for oil, water vapour, carbon monoxide, carbon dioxide and oxygen. One aspect that has been mentioned, however, is that it does not offer simultaneous testing of other contaminants. While it is true that inappropriate positioning of the compressor may lead to the presence of other hazardous substances, it must also be recognised that, under the CoSHH risk assessment requirements, these hazards should have already been identified. This, therefore, eliminates the requirement to check for other contaminants within the supplied air, as any potential hazard will have already been controlled.

Unlike laboratory analysis methods, the F3000 measures a live, representative sample and, by conducting a real-time, continuous test, it stresses the system filtration to the same degree as that encountered in use. As a result, the test becomes representative of actual conditions. This cannot be achieved by collecting a small static sample for laboratory analysis.

The measurement of low moisture levels, which is usually associated with dewpoint monitors, is also easily achieved. With a built in thermometer to record both ambient and airline temperatures, the F3000 will also record airline moisture levels using a detector tube. From this, the dewpoint can be quickly calculated. For example:

A tube reading of 1500 mg/[m.sup.3] and an airline pressure of 5 bar would give a pressure dewpoint of 8[degrees]C. Therefore, to ensure compliance to the requirements, the ambient temperature in which the system can be used must be at least 5[degrees]C higher than the figure, i.e. 13[degrees]C. This can be compared with the ambient temperature recorded during the test to establish a pass or fail.

Featuring an integral electronic sensor with a digital readout to measure oxygen content, it also utilises a built in flow meter which allows verification of airflows up to 600l/min. Lightweight, compact and incorporating a user-friendly menu-driven display, the unit has a low power consumption requirement, thereby eliminating the need for lengthy, frequent recharging. Supplied complete with a programmable test facility for both mineral and synthetic oils, it can be used with low-pressure airline breathing systems as well as high-pressure regulator assemblies to test HP cylinders.

The requirements of BS4275 are clear: when tested at a pressure of
1 bar absolute, the breathing gas supplied to the wearer should
meet the following criteria

Substance              Criteria

Oxygen (O2)            20-22% by volume (dry air)

Carbon monoxide (CO)   5ppm (5 ml/[m.sup.3]) max

Carbon dioxide (CO2)   500ppm (500 ml/[m.sup.3]) max

Oil mist               0.5 mg/[m.sup.3] max

Odour/taste            Without significant odour or taste

Contaminants           No substance should be present at
                       a concentration > 1/10 of the assigned
                       OEL or users' internal OEL

Water (liquid)         There should be no free liquid water

Water (vapour)         HP Cylinders:

                       40-200 bar: 50mg/[m.sup.3] max, above
                       200 bar 35mg/[m.sup.3] max

                       Cylinder Charging Compressor:
                       25mg/[m.sup.3] max

                       Airline below 40 bar:

                       Pressure dewpoint to be 5[degrees]C below
                       likely lowest ambient temperature. Where
                       temperature is not known then pressure
                       dewpoint should not exceed -11[degrees]C
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Publication:Plant & Works Engineering
Date:May 1, 2004
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