The future of occupational hygiene?

fortune teller

Last week I was over at the American Industrial Hygiene Conference and Exhibition (AIHce) in San Antonio, Texas. It was my first time at this event and it was a great experience.

This year is the 75th anniversary of the American Industrial Hygiene Association so this was an opportunity to look back on what the organisation has achieved. But they didn’t just rest on their laurels. it’s important to keep an eye on the future too, and this is what they did. Two of the keynotes in particular looked at what is happening in society and the world of Industrial/Occupational hygiene and at developments that are already starting to happen and which are likely to change the way we live and work in the not too distant future.

The first Keynote speaker, on the Monday morning, was Peter Leyden, former Managing Editor at Wired Magazine, CEO of the Reinventors Network and a Silicon Valley entrepreneur. His talk focused on how big technology paradigm shifts are changing our world. First, he took a look at other periods, such as after the Great Depression in the 1930’s, that faced similar changes. He went on to discuss  the major transformations that are taking place in the 21st Century – the digital revolution, the future of video, demographic changes, global shifts, cleaner energy and politics

“To understand the technological changes that are happening around us, we have to put them in an even bigger context. We’re talking about rhythms of national history, or even world history. We are going through a very rare global transformation. From an American perspective, it’s something we’ve gone through only a handful of times,”

He was optimistic that the “brightest minds” will use the available technologies such as new technologies such as bio tech, nano tech and clean tech industries, to bring innovation forward to solve global problems such as climate change.

People will look back on our time period and say, "That’s when the world went digital, that’s when the world went global, and that’s when the world went sustainable" .

Although he didn’t specifically address what was happening in industrial/occupational hygiene, or how these changes would directly affect it,his talk provided an overview of the context in which we are working and a lot of food for thought.

Some of these ideas were developed the next morning in the Keynote by John Howard. He started by looking back at the development of the Industrial Hygiene profession in the USA and it’s achievements. He then went on to discuss the health effects of emerging manufacturing technologies and how technological innovations in sampling practices will change the profession over the next 75 years.

There have been relatively few changes in how occupational hygienists have measured worker exposure to dust, vapours and other hazardous substances since the development of the personal sampling pump by Jerry Sherwood in the UK in 1957. However, Dr Howard suggested that developments in computer technology and miniaturisation could mean that exposure assessment in the near future could involve continuous sensing of the working environment and that it will be possible to directly monitor chemical loads in workers’ bodies and determine how those exposures have altered them. He suggested that personal direct-reading instruments may be developed that would allow workers to control their own exposures, and that occupational hygiene sampling could even evolve to incorporate the use of sensors that continuously send exposure data to a central database.

His predictions echoed a number of the points made by John Cherie at the British Occupational Hygiene Conference in Nottingham in March. He also suggested that relatively cheap sensors and monitors that connect to devices such as mobile phones, tablets and the Internet, that are already being developed (and in some cases are already available) would change the way that sampling and exposure assessment is carried out by occupational hygienists.

These devices may be less accurate than the traditional sampling methods used to assess personal exposures. But this would be more than compensated for by the massive increase in the amount of data.

I have no doubt that there will be major changes in exposure assessment methodologies in the future. The important thing to remember is that occupational hygiene is about protecting worker health and that understanding exposure is an important step towards ensuring that it is controlled and that we achieve a healthy working environment. Anything that improves the validity of what we do is to be welcomed. Exciting time ahead!


Dust Exposure

There are many common industrial processes which cause workers to be exposed to a wide range of toxic and harmful dusts. Although official statistics are hard to come by, John Cherrie of the Institute of Occupational Medicine has estimated that in Great Britain almost 10 million workers are exposed to dust at work.


Handling of powders usually results in significant release of airborne dust, whether this involves the manual emptying of sacks, manual scooping of powders or mechanical transfer of powders and / or into open containers.


​​Any tasks or processes that involve cutting or abrasion of solid materials will generate dust that will become airborne.


Most of these processes are energetic which means that the dust created will form a cloud that can extend over a significant distance.

​Handling friable materials (i.e. substances that break up easily) can result in the formation of a dust cloud that can lead to significant exposure.


​Common friable materials include :

  • Glass and rock wool
  • Refractory ceramic fibre
  • Cotton, flax and other vegetable fibres
  • Wool

​Disturbing dust settled on surfaces will normally result in at least some of it becoming airborne. ​Using compressed air and sweeping are particularly likely to lead to significant exposures and should be avoided .


Sometimes the problem is obvious, and the sensible thing to do is to introduce controls. But in many cases an accurate assessment requires measurement of exposure. In these cases it’s important to have a “benchmark” against which the results can be compared, otherwise they’re meaningless. In Britain we have Workplace Exposure Limits – these are legal standards and where one has been set for a substance exposure must not exceed the limit. With carcinogens, mutagens and substances that can cause allergic asthma, the requirement is tighter – exposure must be reduced as far as practicable below the limit.

Although a significant number of  toxic dusts have been assigned Workplace Exposure Limits many of the dusts which can cause chronic obstructive pulmonary disease or other non-malignant respiratory disease have historically been viewed as ‘low-toxicity dusts’ and haven’t been assigned limits. In Britain, the guidelines for action to reduce airborne exposure to these dusts (10 mg/m3 for inhalable dust and 4 mg/m3  for respirable dust) are now known to be insufficiently protective. The need for a new exposure limit of 1 mg/m3  of respirable dust has been suggested by some authors and limits for dust exposure are currently under review in the EU. 

The Institute of Occupational Medicine, for example, has recommended that “until safe limits are put in place, employers should aim to keep exposure to respirable dust below 1 mg/m3 and inhalable dust below 5 mg/m³”.  The TUC has advised health and safety representatives that they “should try to ensure that employers follow a precautionary standard of 2.5 mg/m³ for inhalable dust … and 1 mg/m³ for respirable dust.” In Germany, the MAK commission has adopted a limit equivalent to 0.3A mg/m3 respirable, where A is the density of the substance in g/cm3. This is equivalent, for example, to 0.8 mg/m³ for many silicate minerals or 1.2 mg/m³ for titanium dioxide. All three bodies therefore regard 1 mg/m³ respirable as a more appropriate guideline than the 4 mg/m3 COSHH trigger.

A commentary in a recent edition of the Annals of Occupational Hygiene discusses the background in more detail.


It’s a controversial issue, but my personal view is that working to 10 mg/m3 and 4 mg/m3 trigger values doesn’t provide adequate protection. Some employers might be concerned that working to lower levels would be costly, but in my experience it’s possible in most cases to reduce exposures to well below the widely used “triggers” by employing standard good practice approaches.

Putting measurements into context

2012-05-11 14.09.03

A copy of William Blakes’s iconic monotype print of Isaac Newton is one of the works selected by Marianne Faithfull  for the DLA Piper Series: Innocence and Experience, exhibition  being shown at Tate Liverpool until 2 September.

It’s unusual for scientists to be portrayed in art, and at first glance Newton appears as a heroic figure. He’s sitting on a rock, apparently under the sea, concentrating intently on his work, leaning over a scroll, using a set of compasses, producing geometric drawings. But  he is ignoring his surroundings, turning his back upon the beauty of the natural world.

According to the Tate’s website:

Blake …….. was critical of reductive scientific thought. In this picture, the straight lines and sharp angles of Newton’s profile suggest that he cannot see beyond the rules of his compass. Behind him, the colourful, textured rock may be seen to represent the creative world, to which he is blind.

For Blake, Newton personified a materialist world view where everything can be investigated, measured and categorised in opposition to his own belief in the importance of imagination, emotion, and mysticism.

I think there’s some interesting points here that could be applied to occupational hygiene. An important part of our work is undertaking measurements to evaluate exposures to hazardous agents.  But there’s a danger here that we can become a little like Blake’s Newton. We can become obsessed with the “accuracy” of the measurements and in gathering numbers.

Now, while I think it is important that our measurements are “accurate”, just how accurate do they need to be? If we are comparing with a limit of, say, 100 ppm, do we really need to know whether the concentration is 99 or 101 ppm? Well, given the large range of variability in workplace exposures, in both of those cases I’d say there was a problem. And if we’ve only taken a few samples (which would normally be the case) I’d probably be looking to improve controls  even if the results from a small survey were more than about 25% of the limit.

And that’s the key point really. Occupational hygiene isn’t about measurement – it’s about control. I’d agree with one of the statements made by Lawrence Waterman, who gave the Warner lecture that opened the BOHS Conference in Cardiff earlier this year, paraphrasing Karl Marx

“Occupational hygienists have measured exposure; the point is to control it”

Measurements are important, but they’re a means to an end, not the end in themselves. And given that with most surveys  we will normally have only taken a small number of samples, in order to interpret the results we need to know what was going on when they were taken. We need to gather what is often called the “contextual information” – details on the process, what specific tasks the individual workers were carrying out, what controls were in place, environmental conditions and anything else that could have an influence on exposure.

When evaluating exposure we need to use “multiple sources of evidence”. Exposure measurements are usually a key element of this, but we also need to observe what’s going on, talk to people to get an understanding of the process and how it’s being carried out on the day, check control measures and gather other relevant information. By doing that we can build a more complete picture to help us understand how exposure is occurring and whether control needs to be improved. If we don’t, we can end up like Blake’s Newton, obsessing over measurements while ignoring what’s going on around us and failing to understand the world.

Sampling for Sulphuric Acid Mist

Tomorrow I’m travelling over to Leeds to attend a seminar organised by the Chemical Industries Association seminar  on Controlling and Measuring Occupational Exposure to sulphuric acid mist. I’ll be making a brief presentation on sampling methodologies. I’ve uploaded a copy of the presentation to my Slideshare site, and it can be viewed below.

Exposure to sulphuric acid mist can occur in a number of industries including during sulphuric acid manufacture, loading and unloading tankers, transfer between storage vessels, charging lead acid batteries, pickling and plating operations and other processes.


A new Workplace Exposure Limit (WEL) for sulphuric acid mist came into force in December last year when the UK implemented the latest batch of European indicative occupational exposure limit values (IOELVs). The most notable feature about this WEL, besides having a low value of 0.05 mg/m3, the limit refers to the thoracic fraction. This is the first thoracic limit that has been set, all other particulate WELs being for either the inhalable or respirable fractions.


It is questionable whether a thoracic limit is appropriate for sulphuric acid. The main concern, besides upper respiratory tract irritation, is the potential for tumour formation in the respiratory tract, believed to be a consequence of sustained tissue inflammation and repair processes, with the larynx the main site of concern. As the thoracic fraction excludes particles that don’t penetrate beyond the larynx, it doesn’t really seem appropriate for a limit to be set that excludes the main particles of concern. The original recommendation from SCOEL (the European Union’s Scientific Committee on Occupational Exposure Limits) was for a limit based on the inhalable fraction, but by the time it reached the EU Council it had become a thoracic limit and that’s what ended up in the EU directive and, ultimately, as a UK WEL.


The difficulty the thoracic limit presents is that, currently, we don’t have a validated method for measuring the thoracic fraction of the mist. There are some options, but work needs to be done to determine which method is most suitable and to properly validate it. Given the current political climate with major cutbacks in expenditure by the Health and Safety Executive, I think it’s highly unlikely that they’ll fund this.

The easiest approach is to carry out sampling for the inhalable fraction. If the results are below 0.05 mg/m3, then as the thoracic is a sub fraction of the inhalable convention, then they would demonstrate compliance with the WEL. If the results are substantially greater than 0.05 mg/m3, then there’s a good chance that the WEL will have been exceeded and additional controls need to be introduced. However it would be difficult to interpret results that are only just higher than 0.05 mg/m3.

Sampling for sulphuric acid mist version for slideshare

View more presentations from Mike Slater
  1. European Commission, Employment, Social Affairs and Inclusion, January 2007 Recommendation from the Scientific Committee on Occupational Exposure Limits for sulphuric acid SCOEL/SUM/105
  2. Health and Safety Executive, 2011, EH40/2005 Workplace Exposure Limits, Second Edition

How many samples?


As I’ve discussed in a previous post, there are many factors which lead to a wide variation in exposure for workers carrying out the same job. One implication of this is that it is very dangerous to draw conclusions from one or two samples. But how many samples need to be taken to ensure that exposure is adequately characterised? In practice, it’s difficult to draw up general rules which can be applied in every situation.

Over the last couple of years the British Occupational Hygiene Society in conjunction with their sister organisation in the Netherlands, Nederlandse Vereniging van Arbeidsdeskundigen, have been working on preparing some guidance on sampling strategy for occupational hygienists. This has now been published and can be viewed or downloaded from here. Recommendations are made on the number of samples that should be taken during a two stage approach to be used specifically for testing compliance with exposure limits.

  1. Take 3 representative personal exposure measurements from random workers in the SEG. If all three exposures are <0.1xOEL, it can be assumed that the OEL is complied with.
  2. Do a group compliance test. Take at least 6 more samples from the SEG, at least 2 per worker from workers picked at random. Then carry out a statistical analysis on all 9 results

I think that the science on which the guidance is based is sound, but I doubt that the approach set out is practicable for most organisations. The problem isn’t so much the number of samples (although the analytical costs could be a problem in some cases), but the time required to collect them. Following this guidance would probably involve four site visits and many companies wouldn’t be able to justify the cost involved.

So deciding on how many samples to collect can be one of the most difficult aspects of devising a sampling strategy. Although a better picture of exposure will be obtained if a large number of samples are collected,  a little common sense needs to be used, balancing the value of the results against the cost of the survey.