Welcome to Danny Gazzi's blog on occupational hygiene. It's for publishing occasional posts which should help people and organisations to keep up to date with issues affecting health at work.

“Low Toxicity” Dusts

For the last few years, there’s been a growing concern about the health effects of low toxicity, low solubility, dusts (sometimes referred to as “nuisance dusts”).  This is separate from concern about highly toxic dusts such as silica, asbestos, and dusts which contain proteins, etc. etc.

Occupational dust exposure is normally measured in terms of inhalable &/or respirable dust. Inhalable dust includes everything that is breathed in.  Most if this consists of large particles which get deposited in the nose and throat.  It also includes the smaller particles which are drawn down into the lungs, and which form respirable dust.  Under the COSHH Regulations, the UK exposure limits for respirable and inhalable dust are 4 and 10 milligrams per cubic metre (mg/m³) respectively, as 8-hour averages.

In 2004 the HSE commissioned the Institute of Occupational Medicine (IOM) to review the data it had collected over many years on the respiratory function of  miners exposed to coal dust.  When it reported its findings, it had found a link between loss of lung function and exposure to respirable dust, with noticeable effects even when the average exposures, over a working lifetime, were below 1 mg/m³.  In fact, it was not possible to identify a threshold below which no harm was caused.  There was a similar finding with dusts other than coal.  As a result, in 2010 the TUC representatives on the HSE’s Advisory Committee on Toxic Substances (ACTS) called for the exposure limits for all dusts to be reduced to 1 mg/m³ for respirable dust and 2.5 mg/m³ for inhalable dust as an interim measure.  See here.  The HSE considered that only limited benefits would arise from reducing the exposure limits for airborne dusts, and decided not to try and do so. See here.

In 2011, IOM  published a position paper  in which it stated its opinion that stricter limits could and should be applied, and called for employers to keep exposures to respirable and inhalable dust below 1 and 5 mg/m³ respectively.

These types of opinions have been aired for over 20 years.  For example, one paper, based on the effects of dust exposure on rats, predicted that respirable dust levels below 1 mg/m³ could overload the dust clearance mechanism of the lungs  (Morrow, P.E. et al: Chronic Inhalation Study Findings as the basis for Proposing a New Occupational Dust Exposure Limit,  International Journal of Toxicology March/April 1991 10: 279-290).  (I haven’t got access to this paper myself, so I thank Mike Jayjock for drawing it to our attention, and making a summary available in a slideshow of his. See slides 38-46)

In my experience, the respirable dust fraction generally comprises between 10 -20% of inhalable dust, so the current 4 mg/m³ respirable dust limit is irrelevant, as the 10 mg/m³ inhalable dust limit would always be reached first anyway.  I would be interested to hear of any situations where any of you out there have found otherwise.  If this is the case, a cut in exposure limit for respirable dust from 4 to 1 mg/m³ is smaller than it appears, in practice.

The BOHS is is holding a workshop on the Health Effects from Exposure to Low Toxicity Dusts as part of its annual conference this week.  It will be interesting to see what comes out of it.  Even if the scientific argument is won that the dust exposure limits should be reduced, will it happen in the current political climate, with a government that views “Elf and Safety” as purely a burden on business, and the HSE apparently disapproving of any advice that goes beyond the legal minimum standards.

Paving, Road and Highways Supply Chain

I’ve been remiss in not mentioning the HSE Paving, Road and Highways Supply Chain Project earlier.  It was launched in October 2011, and is the successor to the Kerbcutting project.  It’s kept the same homepage at

http://webcommunities.hse.gov.uk/connect.ti/kerbcutting.community/view

Dust exposure from cutting bricks

The reason for the project is the high incidence of occupational ill health in the construction industry, with 4 times as many days lost to that as there are from accidents.  According to the Project leader, half of work-related cancer deaths are in construction, and the industry has a higher prevalence of limb disorders and spine/back disorders than any other.  Respiratory diseases are also significant, including a high proportion of the 500+ estimated UK lung cancer deaths per year caused by exposure to respiratory crystalline silica dust.  In addition, there are high levels of non-fatal conditions such as vibration white finger and noise induced hearing loss.  It’s no wonder that so many of the workforce have to leave the industry as they get older.

Manual handling of kerbstone

By focusing on paving and roads, rather than the whole of construction, they hope to keep the project a manageable size, and to produce noticeable results.

The issue is relevant to most large companies, not just construction, as these will occasionally have road and pavement maintenance carried out on their premises, and are in a good position to encourage, or even insist on, good practice being followed.

For example, the following measures should be used to prevent or control exposure to silica dust:

X-Ray of lungs with silicosis

• substitute silica-containing stone by other materials, e.g. plastic kerbstones
• where cutting is required, have stones cut to size before they are brought to site, where ventilation controls are more practical
• use water suppression

The Project is looking for volunteers for their 3 working groups, or at least they were.  The working groups are:

• Risk Matrix
• Health Surveillance and Monitoring
• Client & Designer

For details of how to apply, see their website.

———————–

23 May 2012

Update: The  Terms of Reference and the Minutes of the 1st Meeting,  held on 19th March, are now available on the HSE’s Communities website.  One point that strikes me is that it’s a pity that there is no trade union representative on the working group, as communication with the people who are at risk is a key factor.

Controlling Solder Fume (& other small scale emissions)

.

Exposure to solder fume is one of the top 8 causes of occupational asthma in the UK.

A couple of weeks ago, Diamond Environmental posted an article on controlling solder fume on their blog. It’s worth reading, and can be found here: Controlling Solder Fume

To summarise, it says that two of the most common types of extraction controls: flexible arm captor hoods and low volume high velocity (LVHV) tip extraction are usually ineffective at capturing the fume. The former because the captor hood is normally positioned too far away from the work, and the latter because the tube is often not close enough to the tip, and the tubes need cleaning out more often than is usually done or they get blocked up.

It concludes that whenever local exhaust ventilation (LEV) is used as a control method, the best type of hood is usually a partial enclosure which contains the source, and that this is the most effective way of controlling solder fume. Here’s a short video showing how solder fume is contained within a booth.

.
I agree with the article, and I would like to add a couple of further points, and some words of warning.

First the warnings:

In electronics catalogues, one can find “fume absorber units” for use when soldering. These are cheap, but are poor at capturing solder fume, because they don’t enclose the source, and are usually fitted with carbon filters which are practically useless at trapping the fume, so it is just emitted back into the workplace. In my opinion, they should be banned from sale. The HSE could do this with individual suppliers by using Section 6 of the Health and Safety at Work Act, which imposes duties on suppliers etc. so that articles are constructed and designed in such a way that they are safe and without risks to health.

Other, more expensive, filtration systems which recirculate air back into the workplace, in order to reduce heating costs, are usually fitted with HEPA (high efficiency particulate air) filters which are more effective at removing the fume. However, their effectiveness depends on the correct seating of the filter, otherwise the fume can just bypass it, and this should be checked every time the filter is changed. Extracting the air to outside may be safer.

Some further points:

In some cases, an enclosure may get in the worker’s way. To improve accessibility, at least one firm has installed their extraction booths on sliding rails. You can see in the photo that the booth also provides a barrier between the worker’s breathing zone and the fume.

Enclosure hood on rails

This type of booth definitely also has applications for small-scale work other than soldering, e.g. handling small quantities of solvents or powders where a proper fume cupboard is not required.

For soldering, other simple measures can be used to help keep the worker’s head out of the plume of fume, such as using an illuminated magnifying glass. However, this won’t prevent fumes building up in the room.

In most cases where soldering is carried out, measurement of personal exposures is a vital step in the risk assessment, and in evaluating the effect of any changes in the controls used.

(Thanks to Mark Piney for the photo and the video clip)

Formaldehyde in buildings

Irritation caused by formaldehyde in new or refurbished buildings is quite a common problem.  The main sources of the formaldehyde are MDF, plywood, chipboard and fibreboard.  The best prevention method is to ensure that correctly specified materials are used.  Once emitted, formaldehyde vapour can be absorbed by soft furnishings, plasterboard etc., which act as a sink or reservoir, and re-emit it over long periods.

The main symptoms of exposure are irritation of the eyes, nose and throat, together with concentration-dependent discomfort and lachrymation.  It also causes additional concern because it has been classified as a Group 1 human carcinogen by IARC.

The lowest concentration that has been associated with nose and throat irritation after short-term exposure is 80 parts per billion (ppb), although some individuals can sense the presence of formaldehyde at lower concentrations.  The UK has a Workplace Exposure Limit (WEL) for formaldehyde of 2,000 ppb, both as a 15 minute and an 8 hour limit.  Not only is this out of line with most other countries, which have Occupational Exposure Limits of around 300 ppb, but it is inappropriate as a guideline for members of the public and office workers.  The most appropriate guideline in such cases is in the World Health Organisation (WHO) Air quality guidelines for Europe .  To prevent significant sensory irritation in the general population, the concentration of formaldehyde should not exceed 80 ppb (0.1mg per cubic metre) averaged over any 30 minute period. This is also considered to represent an exposure level at which there is a negligible risk of upper respiratory tract cancer in humans.

Here are a couple of recent case studies:

Case Study 1 – Simple Partitions in a Room

Partitions made of MDF and plywood were being erected within a room. The installers, and others who entered the room reported eye irritation and an acrid smell.  At first they suspected the concrete into which they had been drilling, because they first noticed the irritation about 30 minutes after drilling into a particularly hard area, but this turned out to be a red herring.  On a site visit three days later, testing with a colorimetric tube over a ten minute period found a formaldehyde concentration of 1,000 ppb.

The partitions were removed, and the supplier replaced the materials free of charge.  The problem was solved.

..

Case Study 2 – A More Extensive Refurbishment

A building was converted into individual offices with new walls and floors made of plywood, and the walls faced with plasterboard.  About six months after occupation, some staff and members of the public started reporting symptoms of streaming eyes and a metallic taste.  An air survey found concentrations of formaldehyde of 400 – 1,100 ppb, and the offices were closed.  A few months later, Industrial Health Control became involved.  Advice was given to remove soft furnishings, and to increase the temperature and ventilation in order to try and speed up the offgassing.  Logging formaldehyde meters were used to monitor the airborne concentrations.  The formaldehyde levels fluctuated widely, often for no apparent reason, and could be very different in different parts of the building.

Here is one example of the monitoring results over a few days.

Formaldehyde, temperature, humidity monitoring

One immediate point is that monitoring over just a few hours would give a very incomplete picture.  The facilities staff were instructed to open the windows for ventilation each day, as they had to be kept closed at night for security reasons.  You can see on the graph how the concentration falls to nearly zero when this is done, only to rise again after they are closed, and rises even more at the weekend when the windows clearly were not opened.

Over two months the formalehyde concentration fell from  400-1,000 ppb  to 200-750 ppb, and after another two months to 80-200 ppb.  However, this fall then levelled off.  In the end, it was decided to replace the new walls and floors completely.  It has been known to take up to five years to eliminate formaldehyde from a badly contaminated building.

..

..

In order to prevent this sort of formaldehyde problem from arising in the first place, all relevant building materials shouldconform with the Class 1 formaldehyde specification in British Standard BS EN 300:2006[i], when measured in accordance with BS EN 120:1992[ii].

---

[i] BS EN 300:2006. Oriented Strand Boards — Definitions, classification and specifications, British Standards Institution.

[ii] BS EN 120:1992. Wood based panels. Determination of formaldehyde content. Extraction method called the perforator method, British Standards Institution.

Legionnaires’ Disease and Driving

Legionella bacteria are widespread in the natural environment.  When inhaled, usually within fine droplets of contaminated water, they can cause a form of pneumonia called Legionnaires’ Disease, which can be fatal.  The control of this risk has usually focussed on the most likely causes – hot water systems, particularly those with showers, and air conditioning.

Last month, I was surprised by some research published in the European Journal of Epidemiology, which found that the risk of professional drivers getting Legionnaires’ Disease is  5 times higher than the general population.  The main risk factors linked with this appear to be driving through industrial areas, and, in particular, not adding screenwash to the windscreen wiper fluid.  Presumably the latter is due to a preservative biocide contained in most screenwash.  This finding should lead to the review of many legionella COSHH risk assessments, with an obvious action point to anyone who runs a car or any other vehicle.

The article is:

Windscreen wiper fluid without added screenwash in motor vehicles: a newly identified risk factor for Legionnaires’ disease

By: Anders Wallensten , Isabel Oliver, Katherine Ricketts, George Kafatos, James M. Stuart and Carol Joseph

It can be accessed here as HTML, and here as a PDF.

Occupational Hygiene

Occupational hygienists (or “industrial hygienists” in the USA) are involved with the recognition, evaluation and control of workplace health risks. Although hygienists are quite rare animals, the Australian Broadcasting Corporation included them in a series on “Ace Day Jobs”, where you can get a flavour of what the day to day work involves.  Here’s the link and here’s a link to the video of a hygienist describing it. As it’s from Australia, the article mentions the Australian Institute of Occupational Hygienists.  In the UK, the relevant organisation is the BOHS, the British Occupational Hygiene Society, which is open not only to professional hygienists, but to anybody with an interest in the subject.  It’s worth looking at their website if you’re considering a career in occupational hygiene, because they not only describe the possible routes into the profession, but also run a couple of bursary schemes. For people from other countries, you can look at the website of the IOHA,  the International Occupational Hygiene Association, and see if there is a further link to your country.