Question time

21 July 2014

As the British Compressed Air Society’s (BCAS) technical officer, Greg Bordiak is used to dealing with a wide range of questions from both members and end-users. From pressure tests, to correct operating pressures to specifiying the correct air purity level… Greg has been asked it all! Here he answers three of the Society's most frequent questions.

Can you send someone round as my air receiver needs a ‘pressure test?

There is a common misconception that a ‘pressure test’ on an air receiver should be treated as a standalone examination.  In fact, it was way back in 1961 when the last Factories Act was produced that applied to air receivers alone and requirements have clearly moved on since then!

The correct approach is to identify whether the compressed air system has a written scheme of examination as required by the Pressure Systems Safety Regulations (PSSR).

The PSSR, which replaced the Factories Act, states that a compressed air system requires a written scheme of examination (Reg.8), which can then be applied by an examiner (Reg.9). 

As to which technique is used to discover the condition of the air receiver, this will be identified in the written scheme or possibly left to the examiner to choose. If left to the examiner he will decide which method is most suitable taking into consideration the state of the air receiver at the time of the examination.

There are various techniques for examining and assessing the safety of compressed air systems of which a pressure test is only one.  With the introduction of the Hazardous Waste Regulations for example, customers and suppliers have to think carefully about the disposal of waste or oily water and whether they have a license from the local authority to discharge trade effluent. 

In short, if there is no written scheme then the compressed air system is being operated illegally and no examination can take place.

What pressure should my blow gun run at?

Before advising on any pressure levels, the real question to ask is whether operatives are fully advised on how to use a blow gun safely and responsibly.

Areas that should always be explored first are whether the blowguns that are on site have safety features built in and whether the correct types of PPE have been specified and are being worn? 

It is possible that there is a need to use blowguns at general factory air pressure so that there is enough energy to carry out the work required. Thankfully, there are a large number of safety type blowguns on the market but there is still a large installed base of the old style, non-safety models. 

It is important that the guns are regularly inspected and serviced to ensure that they still function correctly and that none of the safety features have been overridden.  It is also essential that the guns are operated correctly and only used for the purpose they are intended for. To illustrate, someone with a small wound or cut on the hand or arms could sustain severe injury if a blowgun operating at just six bar or below strikes that part of the body.

Another question to ask is whether staff that are using non-safety pattern type guns have been instructed in their safe use. As a general rule, the pressure on these should be limited to two bar and insist that all operatives wear protective clothing. 

The use of blowguns should be considered carefully.  Training in safe operation is essential, their continued correct use should be monitored and most importantly they should be maintained regularly in accordance with the manufacturer's instructions to ensure that the safety features still function.

Is there a standard that identifies the contaminant limits for various applications?

Compressed air is a utility necessary in most industries, but considering it as such can undermine the importance of the air’s purity levels and the impact this can have on critical processes.  A paint finish may be capable of rectification but a spoiled silicon chip can only be thrown away. 

It is commonly assumed that there are standards that identify the contaminant limits for an application.  In the case of ISO 8753-1, the standard actually comprises a 

a menu of contaminant levels for the three most common types; particles, water and oil. 

The contaminants are classified into groups of convenient values so that the user and the supplier can develop a solution for an application based on standard levels of contamination. The means to provide the necessary air treatment equipment can then be determined on either a general configuration or as a specific solution. Each of the contaminants needs to be identified with its acceptable limit chosen from ISO 8573-1 classification that suits the application.

In some application areas there are publicly available good practice guides that identify the combination of contaminant levels acceptable. The food and beverage industries have such a guide produced by BCAS, known as the Food Grade Compressed Air Best Practice Guide. There are other areas such as the health, medical and dentistry which have their own specifications. Breathing air is identified in a European Standard and there are others. 

For many applications however, there are no commonly available specifications for compressed air. This is when ISO 8573-1 comes in useful as it helps the user of compressed air to identify the contaminant classification and, by discussion with a supplier, determine the correct and economic levels. 

In doing so, this will enable discussions around the most practical and affordable way of achieving the purity level required.  Achieving a classification of 1:1:1 sounds good, but it is also expensive to maintain such levels. Trying to maintain -700C pdp (desert type values) in a compressed air system made up of many hundreds of metres of piping is possible but will be very costly, take days to reach that low level and still be susceptible to fluctuations.