What’s a thorough examination and test?

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Companies that have installed local exhaust ventilation systems have to undertake a “thorough examination and test” (TExT) at least once every 14 months. The objective of the TExT is to find any significant defects and to have them remedied to regain control. In most cases they will employ an external organisation to carry out these tests so that they can meet their legal obligations. There are a large number of companies offering this service – sadly not all of them do a proper job. Sometimes this is due to a lack of competence but it may also be because the test engineers are under pressure to test systems quickly to maximise the number of tests they can carry out during the day. Unfortunately that leads to corners being cut and too many testing companies carry out a minimal, rather than a thorough test.

One of our consultants was visiting a client recently to carry out ventilation testing on a system used to control fume generated during brazing operations in a plumbing shop. It consisted of 8 individual flexible arm captor hoods connected to a main duct from the fan (see photograph below). As I’ve discussed in a previous post, captor hoods are rarely effective at controlling contaminants and other types of hood are usually preferable. The ductwork design, with no attempt at balancing, means that it would be difficult to achieve the same velocity in each branch.  However, in this case, the design would probably be adequate providing management ensured that the users positioned the hoods are carefully over the plume of fume generated during brazing and the appropriate capture velocity could be achieved in each leg.

The system had previously been tested by another company and our consultant asked to see the report. He needed this so he could compare his results with those from the previous test so that he could determine whether there was any deterioration in the system’s performance. The report he was given (see below) was a good example – of an inadequate test report.

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Guidance on what should be done during a TExT is provided in the Health and Safety Executive’s document HSG258 Controlling airborne contaminants at work: A guide to local exhaust ventilation. This advises that a TExT will normally involve three stages:

  1. A thorough visual examination to verify the LEV is in efficient working order, in good repair and in a clean condition.
  2. Measuring and examining the technical performance to check conformity with commissioning data. Even on a simple system this would normally include determining hood capture and face velocities and duct velocities and measuring static pressure at behind all hoods and across the air cleaner (where present) and fan.
  3. An assessment to check the control of worker exposure is adequate. At the very least, this will involve the use of smoke tubes or a dust lamp.

Of course it isn’t always possible to carry out all the tests recommended in HSG258 due to design, safety and practical considerations. Nevertheless a proper TExT, even on a simple system, will involve a number of different measurements and tests.

For the multi branch system, as in this case, I’d expect a TExT to involve, as a minimum, the following:

  • a thorough visual examination
  • a smoke test on each hood as a way of checking on how effective they were at capturing the fume generated by the brazing process
  • capture velocities measured on each hood at the point further from the hood where the contaminant could be generated
  • face velocities measured at each hood
  • static pressures measured behind each hood
  • measurement of the duct velocity in the main branch (it may not be necessary to measure duct velocities in each branch
  • the static pressure across the fan
  • checking the fan to ensure that it is rotating in the correct direction

The test carried out by the engineer from the previous company involved only a visual examination and measurement of duct velocities. According to the report, an assessment of control had been made from these results. Not only was the scope of the testing inadequate, the report states that the duct velocity had been measured using a vane anemometer. This is an inappropriate instrument for this type of test. I suspect the engineer had placed the anemometer at the entry to the duct inside the hood. Not only is this not the best way to measure duct velocity, It would be difficult to position the anemometer properly to measure the flow into the duct.

The “duct” velocities given in the report are all around 10 m/s. That would be adequate for conveying fume, but would the contaminants be captured effectively? No face or capture velocities are provided. If the hoods were used as receptors, and were positioned very carefully above the plume of contaminants, there was a chance that the system would achieve adequate control. But this would need to be verified by observations of the process and, ideally, a smoke test. Neither was done.  It’s probably more likely that the arms would be used a capture hoods. In that case it would be necessary to check that the capture velocity was adequate. With moveable hoods of this type the best approach would be to determine the distance from the hood face where the minimum acceptable capture velocity could be achieved and include that in the report so that the user could be informed. There is nothing in the test report to suggest any of these important measurements were done.

In my view, the original report was inadequate. More time was needed to carry out a proper thorough examination and test. No doubt their company charged the client considerably less than we did – but, as with most things in life, you get what you pay for.

Even when an outside company is employed to carry out TExT the legal obligation to ensure that the test is thorough remains with the owner of the system. So they need to ensure that they’re using a competent company who will carry out the test properly in accordance with HSE’s guidelines.  Its important for employers to ensure that they employ a company who will do a proper job.

Controlling solder fume

In a previous post I discussed the health risks associated with exposure to the fume generated during soldering with rosin cored solder. It’s a respiratory sensitiser, and is one of the main causes of occupational asthma in Great Britain.

The fume is generated due to thermal degradation of the flux – usually containing colophony (also known as rosin), which is manufactured from pine resin, and is usually contained within the soldering wire (rosin cored solder.   The flux is needed to prevent oxidation of components, remove contaminants from the surface of the components, and reduce the surface tension of the molten solder. When heated during soldering it vapourises and condenses into fine particles, which form the fume which is usually clearly visible as a white smoke. Thermal degradation of the colophony also generates irritant gases.

In an ideal world we would try to eliminate the risk by using an alternative, rosin free flux. However, this is difficult in practice and most alternatives I’ve come across still generate harmful fume. The amount of fume can be reduced by controlling the soldering temperature. However some fume will still be evolved. So local exhaust ventilation is likely to be needed to minimise the risk to health whenever soldering is being undertaken.

One of the most common type of of extraction system used in workplaces where soldering takes place is the flexible arm captor hood. As I’ve described in a previous post, the problem with external captor hoods like this is that airflow drops off very rapidly with distance from the face of the hood. Positioning is crucial, particularly with solder fume which is hot and rises in a narrow plume before dispersing. Operators tend to position the hoods too far away from the source as moving them close enough would obstruct and interfere with their work. Also, any ambient air movement in the workplace can disrupt the airflow from the extraction, further reducing their ability to capture the fume. Consequently, this type of system is usually ineffective at controlling exposure.

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Another common approach is to install a low volume high velocity (LVHV) system. Here, a small metal tube is attached to the soldering iron, the idea being to capture the fume close to source. The metal tube is then connected to extract ducting via flexible plastic tubing. In principal this should be much more effective then using the flexible arm hoods.

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However, there are a couple of problems which often render these ineffective. First of all operators rarely position the tube close enough to the tip of the soldering iron where the fume is generated, pleading that the tubes “gets in the way of the work”. Secondly, fume that is captured condenses out inside the metal tube and the associated plastic tubing. Unless these are cleaned out very regularly (and, in my experience, this rarely happens) airflow is seriously restricted, significantly reducing the capture velocity and the degree of control.

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Whenever local exhaust ventilation is being applied to attempt to control exposure to airborne contaminants, the best type of hood will usually be a partial enclosure which contains the source. In that case the contaminant doesn’t have to be captured – it is generated within the hood.  If sufficient airflow is provided to draw the contaminant away, and prevent it escaping from inside the hood, there is a good chance that effective control will be achieved. In the past, this approach has not typically been applied to soldering. However one company, working in conjunction with Health and safety Executive Inspectors, has developed such a solution.

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Here, the booth is large enough to contain the work, without interfering with the task. It is constructed of transparent material, so the operator can clearly see what she is doing, while presenting a barrier between the fume and her “breathing zone”. The enclosure also minimises local air turbulence and draughts so that the solder fume rises within the enclosure, relatively undisturbed, and is then captured by the extraction, preventing the operator being exposed to the fume.

This type of hood is by far the most effective way of controlling exposure to solder fume and really needs to become the standard approach for the electronics industry. It is recommended by the HSE in their COSHH Essentials Control Sheet for soldering. Unfortunately employers tend to be quite conservative. Systems with captor hoods have been widely used for many years and it is not easy to convince employers that they’re not the most appropriate approach – particularly when they’ve spent a lot of money purchasing and installing them.

(Note: HSE have produced guidance on the hazards and legal requirements and on the control of rosin cored solder fume.)

Designing and managing local exhaust ventilation

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Local exhaust ventilation (LEV) is one of the main measures used to control worker exposure to hazardous substances. It’s difficult to work out exactly how many systems there are in Britain, but the Health and Safety Executive carried out some research in 2006 and estimated that there were between 260,000 and 330,000 businesses that have LEV. Now some of these will be small organisations who will only have installed one system but many others will have several systems in place. So, if the HSE’s estimates are still valid, the total number of systems could be approaching half a million.

As with any engineering control (or other plant and equipment for that matter), if LEV is to work effectively it must be well designed and than managed properly.

Sadly, experience suggests that this is rarely the case. In practice

  • Many suppliers fail to consider the nature of the process and the behaviour of the contaminants when designing extraction hoods.
  • Inappropriate, “off the shelf” systems are installed
  • Proper commissioning is rarely undertaken.
  • Most suppliers don’t provide detailed instructions and other information needed by the client on use, maintenance and testing.
  • Once systems are installed many companies don’t carry out planned routine maintenance and testing.
  • Where testing is carried out it normally only comprises an annual “thorough examination and test” with no interim checks on condition or performance.
  • The standard of the “thorough examination and test” is often poor. Many testing companies only carry out flow and pressure measurements and do not evaluate the effectiveness of the system at controlling the contaminants.

The HSE recognised these problems and, following extensive stakeholder consultation, published updated guidance in HSG258 Controlling airborne contaminants at work: A guide to local exhaust ventilation.

I’ve uploaded a presentation to Slideshare about “Effective design and management of LEV” which summarises many of the key points from HSG258.

To attempt to improve awareness of good practice amongst managers a new one day BOHS Approved course – Practical Management of LEV Controls has been developed in conjunction with HSE. We’re going to be running it on 15th September 2011 in Chester. Cost £195.00 plus VAT per delegate (includes course documents, lecture fees and lunch). The above presentation gives a flavour of the course content.

To test or not to test?

I recently received the following query from a client:

“I have come across various items of equipment which appear to have integral LEV types of arrangement ……..  All have been introduced to reduce the level of dust or chemical that may have a deleterious effect on the user of the equipment.  I am unsure if all are considered strictly LEV and subject to the 14 month inspection period.  Having asked a number of the manufacturers of the equipment if the LEV has been designed  and confirmed to reduce exposure adequately, they often reply that it was included as a desirable attempt at reducing exposure.  Where does this leave me?  Should I be getting the LEV commissioned and deemed appropriate?  For the majority of equipment the requirement to adequately maintain it under PUWER has meant that it is regularly serviced, but is this enough in relation to the LEV component?”

I think we sometimes get hung up about LEV. In fact Regulation 9 of COSHH requires maintenance of ALL controls and a regular thorough examination and test of all ENGINEERING controls. (see COSHH Reg 9.2 which states

“ Where engineering controls are provided to meet the requirements of regulation 7, the employer shall ensure that thorough examination and testing of those controls is carried out”

The only difference for “LEV” is that the maximum interval is specified and some specific guidance on what this should involve and other aspects of managing the control is available. In fact the general  principles set out in HSG258 regarding the management of LEV (commissioning, maintenance and testing) are really relevant to all engineering controls. LEV is only singled out because it is a common control where these aspects are particularly important if the system is to be effective.

Servicing in accordance with PUWER is unlikely to properly address the LEV. It may ensure that the fan works, for example, but the most important aspect of LEV testing is to verify  that the contaminants are being controlled, and this will almost certainly not be done.

So I think the good practice set out in HSG 258 is relevant to the systems mentioned by the client, although the concept of “reasonable practicability” should be applied when deciding exactly what is needed and how urgently the issue is addressed. Some systems will be more important than others in respect to controlling exposure and it would be best to identify these and prioritise them. Also the amount of work involved will depend on the design of the system.

In the case of simple systems used to control low concentrations of contaminants  it may only be necessary to introduce  smoke testing and a few basic measurements in addition to what you are already doing. However, more complex systems used to control higher concentrations of more hazardous substances are likely to need a more substantial test.

Of course, this is only my personal view. A HSE Inspector may have a different interpretation!

Testing walk-in spray booths

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Spray painting inside a walk-in booth (photo credit: HSE)

We recently received a query from a client who carry out paint spraying of isocyanate based two pack paints in a large walk-in type spray booth. They wanted us to carry out sampling to help them to decide when it was safe to enter the booth without their workers wearing their air fed masks. This sounds like a good idea. In fact it’s essential for workers to know when the paint spray has been completely cleared from the booth. Isocyanates are very potent respiratory sensitisers causing asthma in susceptible individuals. Anyone sensitised to isocyanates will experience asthmatic symptoms even if they are only exposed to very low concentrations. However, air sampling isn’t the best way to determine the “clearance time”.

If it was possible to use a direct reading instrument that gives a reading of the instantaneous concentration it would be relatively easy to determine when the booth was cleared. Unfortunately there isn’t a direct reading instrument that can be used for isocyanates. Sampling has to be carried out using an integrating technique – that means that a sample is collected over a period of time, and, after it has been analysed in a laboratory, it is then possible to determine the average concentration present during the sampling period. To determine the  “clearance time” a series of samples would have to be taken one after another. This would be expensive (the analysis isn’t cheap) and the standard method for isocyanates is not particularly good. The samples are collected by bubbling air through a reagent dissolved in toluene and as a low detection limit would be required it’s difficult to take samples over a short period.

Consequently its better to use a different approach, releasing smoke into the enclosure and then timing how long it takes for it to be completely removed from the booth. This method is quicker, less messy and much less expensive. The test can also be used to check that there are no leaks from the booth – any smoke escaping should be clearly visible. The Health and Safety Executive explain how to carry out this test in their publication “Controlling isocyanate exposure in spray booths and spray rooms” which can be downloaded from their website here.

The following videos show a smoke test taking place in a typical booth.

Once the clearance time has been established it’s important to ensure that anyone who works in the booth is informed and a notice posted at the entrance to the booth, something like this:

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The HSE would like to see automatic clearance time indicator fitted on walk-in spray booths, but in my experience few have them. This is something that should really be addressed by the manufacturers and suppliers of the equipment. A new booth should already have them fitted, and clearance times should be established during the commissioning of the equipment after it’s been installed.

Following on from the initial test checking the clearance time should also form part of the statutory thorough examination and test required for LEV systems under COSHH Regulation 9. All engineering controls deteriorate over time, so the time taken for the contaminants to clear is likely to increase, even with a well maintained booth.

Glove boxes

Glove boxes are often used in the pharmaceutical industry to control highly toxic “active” agents used in drug formulations. In principle they should provide a high degree of protection for the user. The contaminant is completely contained inside an extracted enclosure while the worker is outside. So when we’re carrying out a risk assessment and spot that the work is carried out inside a glove box we might assume that exposure will be well controlled. However, we have to be careful – sometimes the opposite is true.

positive pressure glove box

Looking at the above picture you can see that the gloves are sticking out of the enclosure. This is a good indication that the enclosure is under positive pressure. This means that contaminated air will leak out through any gaps or breaches in containment, potentially bringing contaminants out with it to which the operator will be exposed.

Such “positive pressure” booths are often used for quality considerations – to protect the product from contamination – and this is probably the case here.