Health in Construction

A couple of weeks ago I travelled down to Birmngham to give a talk on behalf of the BOHS Breathe Freely initiative at the Health and Wellbeing event at the NEC. The Title of the talk was Managing Health in Construction – What Good Looks Like. An annotated version of the slides I used during the talk are now available on Slideshare

To prepare for the talk I did a little research on the meaures that are readily available to control exposure to contaminants, particularly dust, during common activities on construction sites. A number of studies have been done, both on-site and in the laboratory to assess the effectiveness of water supression and on-tool extraction for power tools. These studies have confirmed just how they can be.

For example

  • A large scale study in Ireland by Healy et al showed that the use of local extraction built into on-tool shrouds could reduce dust exposures by up to 99%
  • Laboratory tests by Thorpe et al showed water suppression on cut-off saws reduced dust levels by up to 99%

Despite this, in a large proportion of cases these engineering controls are not being used with reliance placed on respiratory protection which is often incorrectly used and inadequately managed. So one of the main aims of the BOHS Breathe Freely initiative is to raise awareness of the types of controls that can be used to reduce exposure. Hopefully in the not too distant future we’ll see water supression and on-tool extraction become the norm rather than the exception.

 

References

Measurements of the E€ectiveness of Dust Control on Cut-off€ Saws Used in the Construction Industry. Thorpe et al. Ann Occup Hyg Vol. 43, No. 7, pp. 443-456, 1999

An Evaluation of On-Tool Shrouds for Controlling Respirable Crystalline Silica in Restoration Stone Work.  Healy et al. Ann Occup Hyg 2014;58:1155-1167

Silica exposure in the construction industry

One of the most important health risks encountered by construction workers is exposure to respirable crystalline silica dust. Crystalline silica, mainly in the form of quartz, is the main component of most rocks, sands and clays. In the construction industry it can be found in  stone, concrete, aggregates, mortars and other materials.

Respirable particles (smaller than 10 microns in diameter) of crystalline silica,  which are produced during many common activities such as cutting, blasting or drilling granite, sandstone, slate, brick or concrete, penetrate deep down into the lungs where they can cause serious damage. Regular, repeated exposure to respirable crystalline silica can lead to silicosis, a debilitating lung disease, chronic obstructive pulmonary disorders (COPD) and lung cancer. It usually takes many years of exposure to silica dust before these symptoms start.

A couple of weeks ago I was giving a talk to a meeting of safety consultants on the BOHS breathefreely initative and decided to include some discussion on silica exposures in the industry. Unfortunatly no major study has been carried out in the UK. However, there are several detailed papers on exposures in the industry in some comparable countries in the Annals of Occupational Hygiene and other journals, so I was able to include some figures in my talk.

The research has shown that many of the common activities undertaken in the construction industy lead to exposures well in excess of the UK Workplace Exposure Linit of 0.1 mg/m3 for respirable silica – and this isn’t a “safe limit” with an estimated 2.5% of workers exposed to this concentration for only 15 years developing silicosis. Yet for most of the common operations where workers are at risk from exposure to silica, there are control measures available that are usually relatively straight forward to implement.

Dark Satanic Mills

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Many people when they get to a certain age start to wonder where they came from. That was certainly true for me so a few years ago I started to research my family tree. Although there were a few surprises my research confirmed that I my family were ordinary workers. I wanted to find out about my roots, about my ancestors, where they came from and how they lived. And as an occupational hygienist I couldn’t help but be interested in what they did for a living and their working conditions.

Halifax Mill Chimneys

Coming from Lancashire it wasn’t a surprise to find that many of my ancestors who lived in the 19th and 20th Centuries were employed at some time during their lives in cotton mills. And working in cotton mills they were faced with a whole host of health risks.

I’ve always been interested in industry and when I was a boy my mother arranged for me to have a look round the mill where she worked. The first thing that hit me when I walked in the mill was the tremendous noise. Levels in weaving sheds were likely to be well above 90 dBA – often approaching, or even exceeding 100 dB(A). Communication was difficult and mill workers soon learned how to lip read and communicating with each other by “mee mawing” – a combination of exaggerated lip movements and miming

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Not surprisingly many cotton workers developed noise induced hearing loss – one study in 1927 suggested that at least 27% of cotton workers in Lancashire suffered some degree of deafness. Personally, I think that’s an underestimation. This is how the term “cloth ears” entered the language – it was well known that workers in the mills were hard of hearing.

This lady is a weaver and is kissing the shuttle – sucking the thread through to load the shuttle ready for weaving.

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This practice presented a number of health risks – the transmission of infectious diseases, such as TB, but as the shuttle would be contaminated with oil, and the oils used then were unrefined mineral oil – there was a risk of developing cancer of the mouth.

Exposure to oil occurred in other ways particularly for workers who had direct contact with machinery or where splashing of oil could occur. There was a high incidence of scrotal cancer in men who operated mule spinners – and this was a problem even in the 1920s. In earlier times workers in mills had to work in bare feet as the irons on their clogs could create sparks which could initiate a fire due to the floorboards being soaked with oil. Contact with these very oil soaked floorboards led to cases of foot cancer.

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And of course there was the dust. Exposure to cotton dust, particularly during early stages of production, can lead to the development of byssinosis – a debilitating respiratory disease. An allergic condition, it was often known as “Monday fever” as symptoms were worst on Mondays, easing off during the week. A study on 1909 reported that around 75% of mill workers suffered from respiratory disease.

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The worst areas for dust exposures were the carding rooms where the cotton was prepared ready for spinning, but dust levels could be high in spinning rooms too.

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Although control measures started to be introduced in the 1920’s workers continued to be exposed to dust levels that could cause byssinosis. Studies in the 1950’s showed  than more than 60% of card room workers developed the disease as well as around 10 to 20% of workers in some spinning rooms.

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A lot of work was devoted to studying dust levels, developing standards and control measures by the early pioneers of occupational hygiene in the UK and I’m sure this contributed to improved conditions in the cotton industry in the UK. I’m not sure I’d like to have to operate their dust sampling kit though – it certainly wasn’t personal sampling!

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Today things are different. The carding machines, spinning frames and looms are silent and have been sent for scrap. The mills have been abandoned and are derelict or demolished or have been converted for other uses.

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Cotton is still in demand but it’s a competitive market and the work has been moved to other countries where labour is cheap and standards are not as high – Africa, China and the Indian sub-continent. Another consequence of globalisation. Although you could say that the industry is returning to where it originated in the days before the industrial revolution. Sadly, conditions and working methods in many workplaces in the developing world are primitive and controls are minimal. It seems like the lessons learned in the 20th Century in the traditional economies are rarely applied so not surprisingly those traditional diseases associated with the industry are re-emerging in developing economies.

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Studies carried out in recent years have shown high incidences of byssinosis in some mills developing countries. One study in Karachi, Pakistan in 2008 found that among 362 textile workers 35.6% had byssinosis. (Prevalence of Byssinosis in Spinning and Textile Workers of Karachi, Pakistan, Archives of Environmental & Occupational Health, Vol. 63, No. 3, 2008 ). A study of textile workers in Ethiopia published in 2010 showed a similar proportion – 38% had developed byssinosis,  with 84.6% of workers in the carding section suffering from the disease

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Another study, this time into textile workers’ noise exposures in Pakistan indicated noise levels in the range 88.4-104 dB(A). 57% were unaware that noise caused hearing damage and almost 50% didn’t wear ear defenders

William Blake wrote of “Dark Satanic Mills” in 1804. This was still a fair description of the working conditions in Lancashire when my ancestors worked in the mills. And I believe its valid today in many workplaces in the developing world.

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It’s not easy to get accurate figures on occupational health in the UK and so much more difficult in the developing world. The best estimate we have (and it’s likely to be an underestimate) is that 2.3 million people die due to accidents at work and work related disease (World health Organisation). And the vast majority of these are due to ill health

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Some occupational hygienists might take a dispassionate, academic interests in dust exposure. But I think most of us are motivated by a genuine desire to prevent ill health at work and improve working conditions. Many of us work in countries where conditions although far from perfect are relatively good. But can we turn a blind eye to what’s happening in the rest of the world?

Personally, I think it’s something we need to be thinking about.

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.

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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.

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

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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.

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​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 .

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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.

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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.

Low Toxicity Dusts–Part 2

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In my last post I discussed the evidence that suggests that the “trigger values” of 10 and 4 mg/m3 that are widely used as such by many occupational hygienists for “low toxicity dusts” where an official Workplace Exposure Limit (WEL) hasn’t been set, are probably too high to prevent ill health in workers. Despite considering the evidence, the HSE’s Advisory Committee on Toxic Substances (ACTS), has decided NOT to take any action other than to recommend an awareness raising campaign for those exposed to dusts to highlight possible risks to health. However, a number of independent experts and the Trade Unions were not happy with this decision. And following the workshop at the recent BOHS Conference in Cardiff, I’m sure that many practising occupational hygienists feel that applying limits of 10 mg/m3 for inhalable dust and 4 mg/m3  for respirable dust is no longer appropriate.

In my experience there are very few workplaces where inhalable dust exposures exceed 10 mg/m3. For most common processes, it is usually “reasonably practicable” to reduce exposure well below this level by applying common engineering controls such as containment, partial containment and well designed local exhaust ventilation. And in some cases simpler measures such as improving housekeeping or the way the job is carried out, may be enough. So I don’t think that it would be too expensive for industry to work to a lower limit. The TUC has recommended values of 2.5 mg/m3 for the inhalable fraction and 1 mg/m3 for the respirable fraction of “low toxicity” dusts as interim limits. I think these are achievable in practice for most companies if they apply industry best practice. This seems a common sense approach which would reduce the risk to health for workers exposed to these dusts.

However, there there is a problem – there are a number  of “poorly soluble dusts of limited cytotoxicity”, to use the HSE’s preferred term, for which WELs have been established using the 10 and 4 mg/m3 values . For example, aluminium oxide, barium sulphate, cellulose, graphite, gypsum starch and titanium dioxide. There’s about 20 in all. If the HSE doesn’t reduce the limits for these substances, and there is no indication that they intend to do that, it may be difficult to convince employers that they need to work to a lower level than the legal limit.

I guess the best approach would be to argue that COSHH requires that even where a limit is set, the “principles of good control practice” set out in in schedule 2a, have to be applied. In my experience, in nearly all cases where we’ve carried out dust surveys there are usually simple measures that can be taken to reduce dust levels, even when exposures are below a WEL.  So, in most cases by implementing common sense measures and established industry good practice it should be possible to reduce exposure down to the TUCs recommended levels, even for those dusts where a WEL with a higher value exists.

Low Toxicity Dusts – Part 1

dust exposure

(Image source: BOHS)

Regulation 2 of COSHH1 states that any dust when present in the workplace at a concentration in air equal to or greater than 10 mg/m3
of inhalable dust or 4 mg/m3 of respirable (as a time-weighted average over an 8-hour period) is considered to be a substance hazardous to health. If the concentration of dust in a workplace exceeds these figures then the requirements of COSHH will apply, including the need to assess the risk to workers and to ensure exposure is prevented or adequately controlled.

The 10 and 4 mg/m3 values are NOT Workplace Exposure Limits (WELs), but, in practice, they are widely used as such by many occupational hygienists for “low toxicity dusts” where a WEL hasn’t been set. This seems like a reasonable thing too do, particularly as these values have been used where WELs have been set for dusts of low toxicity, such as aluminium oxide, barium sulphate and  titanium dioxide.

However, recently, serious doubts have been expressed as to whether this approach is valid and appropriate to protect the health of workers exposed to airborne dust. There is evidence from both animal experiments and industrial experience that relatively low exposure, well below these levels, to “low toxicity” dust (the UK Health and Safety Executive now prefer the term “poorly soluble dusts of limited cytotoxicity”) may cause adverse effects.

Snapshot[4]

At their annual Conference in Cardiff earlier this year, the British Occupational Hygiene Society (BOHS) held a workshop on “low toxicity dusts” to try to advance the debate. The presentations, which summarise the key points made by the speakers can be downloaded from the BOHS website here. The presentations by John Cherrie and Alistair Hay are particularly informative.

Exposure to high concentrations of any dust can overload the normal clearance mechanisms in the lung, leading to inflammation and possible lasting effects. In particular, there is evidence that exposure to many dusts can cause or worsen chronic obstructive pulmonary disease (COPD). According to HSE, 15% of the risk of chronic obstructive pulmonary disease (COPD) is attributable to gases, dusts, vapours, and fumes at work, and 4000 COPD-related deaths in England are due to workplace exposures. High lung burdens of “low toxicity dusts” can also prevent clearance of other, more toxic, particles, leading to a higher risk of other lung diseases.

Too much of any substance will cause harm. The question is, what is “too much”? Unfortunately, for “low toxicity dusts” the evidence is relatively limited.

In 1999 the HSE published a Contract Research Report of work carried out by the Institute of Occupational Medicine (IOM). They developed a mathematical model based on animal experiments  to estimate the no-adverse effect level (the NOAEL) for titanium dioxide, based on avoiding the impairment of dust clearance and the beginning of inflammation. Using the model they derived a human NOAEL of 1.3 mg/m3 .

In his presentation at the BOHS workshop Alastair hay discussed an IOM study on coal-miners, which found that 35 years exposure to 4 mg/m3 respirable could lead to 17% of non-smoking workers experiencing an FEV12 loss of almost a litre, compared with 10% in a non-dust exposed population

The HSE’s Advisory Committee on Toxic Substances (ACTS), considered low toxicity dusts in 2006/7. The outcome was that they decided to take no further action other than to recommend an awareness raising campaign for those exposed to dusts to highlight possible risks to health. A number of independent experts and the Trade Unions were not happy with this decision.

There is also concern about whether the mass concentration is the most appropriate way of evaluating the degree of risk from dust which is probably related to surface area. Exposure to small particles will have a greater effect than the same mass of larger particles of the same dust.

The following charts, extracted from John Cherrie’s presentation at the BOHS Conference show the relationships between pulmonary inflammation and mass (left hand chart) and surface area (right hand chart) for three different dusts

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The data was derived from Donaldson K, Brown D, Clouter A, et al. The pulmonary toxicology of ultrafine particles. J Aerosol Med 2002;15:213–220.

The charts show a fairly clear linear relationship between surface area and inflammation, irrespective of the type of dust.

I suspect that the majority of occupational hygienists who attended the workshop came away convinced that applying limits of 10 mg/m3
for inhalable dust and 4 mg/m3  for respirable dust, whether they are “official” or not, is no longer appropriate. So what limit should be applied to these dusts? I’ll return to this in another post.

Notes:

1 the Control of Substances Hazardous to Health Regulations

2 FEV1 is the “Forced expiratory volume in one second”. This is the amount of air that can forcefully exhaled in one second