COSHH Assessments – 7 key questions


In my last post I discussed the main problems that I often encounter with how COSHH assessments are carried out in practice. These were

  • concentrating on the hazards rather than the risks
  • neglecting to include process generated substances
  • concentrating on inhalation exposures and neglecting other routes
  • lack of emphasis on controls
  • failure to consider measures needed to ensure continued effectiveness of controls

To be “suitable and sufficient” a COSHH assessment needs to address the risks associated with the use of hazardous substances and decide on what measures are needed to reduce them to an acceptable level. The best way to achieve this is to base the assessment on the work. COSHH assessments should be focused on the process or task rather than the substance.

Guidance on risk assessments typically outlines a number of key steps as illustrated in the following flow chart




Although this provides a good overview of the process it is a little vague. In particular, it doesn’t really set out what is involved in the crucial third step – evaluating significant risks.

Some time ago, I sat down and tried to work out exactly what I do when I carry out a COSHH assessment. I concluded that I ask myself a series of questions:

  1. What substances are workers (and others) exposed to?
  2. What harm can these substances cause?
  3. Is exposure significant?
  4. What is currently being done to control exposure?
  5. Is that good enough?
  6. What needs to be done to improve control?
  7. What else needs to be done to ensure that adequate control is maintained? (e.g. testing controls, air monitoring, health surveillance, training etc.)

Let’s have a look at these in a little more detail

1. What substances are workers (and others) exposed to?

  • Starting with the task or process work out what substances are present – including both those substances bought in and those generated by the process (the latter often present the most significant risks).
  • Consider who could be exposed and how – i.e. by what routes (inhalation, skin, ingestion, injection)

2. What harm can these substances cause?

  • For substances bought it should be possible to determine the hazards they can present to health by looking at the label on their containers and the safety data sheet that suppliers must provide.
  • Information on process generated substances might be more difficult to locate, but the Health and Safety Executive publications and their website are often a good place to start.

For many people this is the end of the assessment, but if you stop here you have only identified hazards and haven’t addressed the risks. You need to continue to consider the other questions.

3. Is exposure significant?

This is probably the most difficult question to answer! Bear in mind that with hazardous substances the risk can be represented by the following equation :-


So the key is to try and quantify or estimate the degree of exposure. There are various ways this can be achieved, for example

  • personal air sampling
  • use of direct reading instruments
  • semi-quantitative measurements (e.g. direct reading dust monitors)
  • visualisation techniques (e.g. dust lamp or smoke tubes)
  • observations


The methods used will depend on circumstances. Sometimes observation is enough where it is obvious that improved controls are needed.


Whatever methods are used, a judgement has to be made on whether exposure is “significant” or not. Essentially you need to ask yourself “does something need to be done to reduce exposure?”. If the answer is “yes” then exposure is significant. (This is something I’ll return to in a future post)

4. What is currently being done to control exposure?

This question may be combined with the previous one. In most cases a COSHH assessment will be undertaken for an existing process where there are likely to be controls in place. You’ll need to identify what they are.

With a new process, the initial COSHH assessment should be carried out before the process starts. In that case you’ll need to identify what control options are available.

5. Is that good enough?

This may be asked in conjunction with questions 3 and 4. Once it’s been established what controls are available a judgement needs to be made on whether they are reducing exposure to a low enough level.

6. What needs to be done to improve control?

If existing controls aren’t good enough then, clearly, improvements will need to be made. A COSHH assessment should identify what measures are needed to control exposure.

Even where exposure is below exposure limits if there are ways of improving control they should be considered. For example, if personal protection is being used, even if it is adequate to reduce exposure below exposure limits, an attempt should be made to identify alternative controls.

Also if workers are exposed to carcinogens, mutagens or asthmagens, COSHH requires that exposure should be reduced to the lowest level reasonably practicable below any relevant limit. So in such cases it is particularly important to try to identify any additional controls.

7. What else needs to be done to ensure that adequate control is maintained?

This is probably the most neglected aspect of COSHH assessments even though the Regulations are quite explicit in requiring the assessment to consider what measures are needed to ensure compliance with all the regulations.

There are many examples in industry where expensive control measures are installed only for them to remain unused, used infrequently or used incorrectly thereby rendering them ineffective. To overcome these problems, effective management measures need to be put into place. COSHH Regulations 8 to 12 are about the things employers can and should do to ensure the controls they implement continue to work effectively. So once appropriate controls have been identified, the assessor needs to ask:

  • what needs to be done to ensure that the controls are used properly
  • what maintenance and testing is needed to ensure that engineering controls and personal protective equipment continue to operate effectively and what auditing should be carried out to ensure that the procedures and safe working methods are followed
  • is exposure monitoring and health surveillance needed as additional checks that the controls are effective
  • what information, instruction and training is required to ensure workers know why the controls are needed, how to use them correctly, procedures for reporting faults etc.

Common problems with COSHH assessments

The Control of Substances Hazardous to Health Regulations (COSHH) are undoubtedly the most important legal requirements for occupational hygienists working in Great Britain. They’ve been around for a long time now – the first version being enacted in 1988 – yet, in my experience, there are still many organisations that haven’t completely got to grips with them. One of the main problems is that many employers do not fully understand the Regulations and what they require and often misinterpret them.

In essence, COSHH is relatively straightforward. It simply sets out a framework for the management of risks created by using hazardous substances at work. I’ve often used the following diagram to summarise the main requirements of the Regulations


Employers whose operations involve the use of hazardous substances have to undertake a risk assessment in order to decide on what controls are appropriate. The other measures are then about they need to do to ensure that the controls remain effective (they’re the management controls that I’ve discussed in a previous post).

1. COSHH is about CONTROL

The first mistake employers often make is to forget the real objective of COSHH – i.e. controlling  the risks. They put a lot of work into the assessment, often generating a lot of paperwork, but don’t follow through to implement effective control regimes. The assessment is important – it is needed to establish priorities by deciding on which are the most significant risks, but it is primarily meant to be a tool to allow the employer to develop an action plan. It’s a means to an end not an end in itself.

2. Assess the RISK not the HAZARD

The second common problem is that many employers do not understand how to undertake the assessment.  It is quite common to focus on the substances used taking information from the safety data sheets provided by the suppliers and transferring it to a standard form , in effect, producing a summarised data sheet. This often involves a lot of time and resources, and although such summarised data sheets can be a useful information tool  they are not a risk assessment.

To see why this is the wrong approach it’s useful to take a look at the wording of COSHH regulation 6 which sets out the requirements for the assessment.

‘An employer shall not carry out work which is liable to expose any employees to any substance hazardous to health unless he has

a}made a suitable and sufficient assessment of the risks created by that work to the health of those employees and of the steps that need to be taken to meet the requirements of these Regulations

b) `implemented the steps referred to in sub-paragraph a.”

The key words that I’ve highlighted are “the risks created by the work”. The substances present hazards but, as the Regulations clearly state,  the risks are associated with the use of the substances.

I’ve heard many people state that they have carried out the assessments for all their substances. This normally indicates that they haven’t got it right. It’s not the substances that need to be assessed, but the work involving their use. For example, take a simple case where solvent is used for cleaning purposes. The risks, and the necessary controls,  associated with using a few millilitres applied with a cotton bud are clearly quite different than using several litres of hot solvent in a vapour degreasing bath. It is inappropriate to carry out a risk assessment of the substance – two assessments of two quite different processes are needed.

So the assessment should focus on the process. It should also concentrate on the risk not just the hazard. Risk is often defined as “the probability of harm occurring in practice”. For occupational hygienists it is best summed up by the following equation:


So the hazardous properties are important, but they are only half the story. The key to effective risk assessment, which s often neglected, is understanding the exposure of employees (and anyone else who could be affected by the work).

3. Identify ALL hazardous substances

Most COSHH assessments I’ve seen concentrate only on the substances that are bought in by the company. Yet there can be other substances present which need to be considered such as fumes, dusts and other airborne contaminants generated by the process or reaction products and intermediates in chemical manufacturing. In many cases it is these process generated substances that present the most significant risks, but they are often neglected.

Silica containing dust generated during cutting of paving slabs

4. Consider ALL routes of exposure

Many people carrying out assessments only focus on substances that can be inhaled. But there are other routes by which substances can come into contact with the body and be absorbed. All of these need to be considered.

Skin exposure by immersion (picture source:

Skin exposure is a common problem in industry leading to direct effects on the skin such as irritation, chemical burns and dermatitis and some substances can be absorbed through intact skin (this is something I’ve addressed in a previous post). Ingestion of hazardous substances can sometimes occur – normally due to contamination of foodstuffs, often following skin exposure. Penetration through the skin can occur by injection where workers are handling needles (e.g. healthcare workers) or where the skin has been abraded or otherwise damaged.

5. Identify controls and other management measures

The other common mistake is that employers often do not properly consider the measures needed to control the risks. They forget that controlling risk is the objective of COSHH and that the Regulations specifically require that the assessment must set out “the steps that need to be taken to meet the requirements of …. (the)…Regulations””.  This means that they need to decide on what controls are needed and what other measures might be needed (i.e. on the use, maintenance and testing of controls, air monitoring, health surveillance and information, instruction and training)

The first step in solving a problem is to recognise that it exists, but we then need to decide how to resolve it. I’ve set out some of the common problems with COSHH that I come across; I’ll consider how to avoid them when carrying out a COSHH assessment in my next post.

Reconsidering the “hierarchy of control”– Part 1

We normally take a break from running courses over the summer – most people are more interested in enjoying some time off than attending an intensive week of study. But it was back to business as usual last week delivering the BOHS module M103 “Control of hazardous substances” in Chester. I’ll also be running the international version (the OHTA course W505) over in Ireland in a couple of weeks.

One of the key concepts we cover early in the course is the “hierarchy of control” – a tool used by occupational hygienists and other health and safety professionals to assist with the selection of control measures. It’s fairly obvious that some measures are preferable to others and the hierarchy formalises this idea by providing a structured list of common options in order of preference. The concept has been around since the 1930’s. It appears to have been developed by the industrial hygiene community in the USA and then was adapted for broader health and safety risks.

The underlying principle of the hierarchy is that the best way to achieve control is by addressing the source of the contaminants. If this cannot be achieved or does not resolve the problem then an attempt should be made to control along the transmission path. Only if neither of these can be achieved should the primary control measures be based around the workers themselves.




Another approach is to classify the measures by type as follows (in order of preference)

  • Prevention
  • Engineering Controls
  • Procedural / Organisational Controls
  • Worker Based Controls



Whichever approach is adopted, the same order of priority tends to result when specific measures belonging to the different categories are considered.


The hierarchy is a useful tool, but it must be remembered that in most cases more than one measure will need to be implemented, because

  • exposure can occur via more than one route of exposure (e.g. when workers are using a solvent based product exposure may occur by inhalation of vapours and via skin contact),
  • there are a number of different sources of exposure that need to be controlled,
  • there is a residual risk as, in most cases, an individual measure will not be 100% effective at controlling the contaminants.

The latter point is particularly important.

The best way to use the hierarchy is to start at the top of the list, considering each option in turn and deciding whether it is "reasonably practicable". Once a measure is selected, consideration should be given to whether the residual risk is acceptable. If not further measures will be needed. The process should  be repeated until it is likely that the residual risk is reduced to an acceptable level.

For example, a worker spraying a two pack polyurethane paints in a car body shop can be exposed to isocyanates and solvent vapours by inhalation and is likely to have some skin contact with the paint and solvents.


In the real world it’s unlikely that elimination of the isocyanates by substituting a less hazardous paint would be feasible. Similarly process automation and containment are unlikely to be practicable. So the first measure from the hierarchy likely to be implemented is local exhaust ventilation, normally in the form of a walk-in booth. This would probably be adequate to control the exposure of his colleagues, but as he has to be inside the booth he will still be exposed to high concentrations of contaminants. Consequently there is a significant residual risk, so other controls are needed. The sprayer would need to wear suitable air supplied respiratory protection and good working methods and safe working procedures would also be needed. Personal protective equipment and good working methods would also be needed to minimise skin contact. So a “suite” of control measures is needed to adequately control the risks.

Once the appropriate controls have been selected, other measures will be needed to ensure they continue to be effective. I’ll return to this in another post in the near future.

Monitoring skin exposure to chemicals


Inhalation is normally considered to be the main route by which chemicals can enter the body. Most industrial processes where chemicals are used will create airborne dust clouds or lead to the evolution of vapours and gases which are readily inhaled and then absorbed into the bloodstream via the respiratory system. However, in some cases there is a potential risk from absorption of substances through the skin following dermal exposure, usually due to direct contact with organic liquids but sometimes through absorption of vapours.

Assessing skin exposure isn’t easy. There are well established methods for estimating exposure to most common industrial chemicals by inhalation but there are a number of major difficulties involved in developing a good method for measuring uptake through the skin.

Starting in 2003, a major International conference has been held devoted to the science of skin exposure to chemicals at work and from the environment. BOHS hosted the fourth conference in Edinburgh two years ago. The latest conference was held in Toronto, Canada at the beginning of June. One of the keynote presentations was given by John Cherrie of the Institute of Occupational Medicine, and a former president of the BOHS. He provided a good summary of the current state of knowledge on skin exposure assessment. His presentation has just been posted on Slideshare and can be viewed below.

Image from jelaga @ stock.xchng

Skin Exposure and COSHH Assessments


Recently I’ve been working with a client on a review of their COSHH assessment protocol. Many of their processes involve the handling of lubricants, sealants and adhesives which have a low volatility and present only a minimal risk from inhalation. The main risk of exposure is from skin contact. However we found that their COSHH assessment procedure mainly focuses on inhalation and so, consequently, many of their assessments haven’t properly considered skin contact.

In my experience this is quite often the case. COSHH assessments tend to focus on inhalation exposures. Skin exposures are commonly neglected. Where they are considered controls are usually poor – in most cases personal protection being used.

Skin exposure can lead to two main concerns

  • direct effects on the skin (e.g. irritation, skin burns, skin sensitisation)
  • absorption through the skin, contributing to overall body burden.

Even the HSE’s basic risk assessment tool, COSHH Essentials, doesn’t properly consider these risks. Skin hazards are identified if the substances have been assigned the appropriate R phrase for skin effects, but skin absorption is not considered. Even where skin effects are identified, the output from COSHH Essentials will recommend the use of PPE, which should really be the last resort, not the only solution suggested.

According to the HSE

  • In 2009/10, an estimated 22,000 individuals reported experiencing “skin problems” which they believed to be work-related, according to the Labour Force Survey.
  • There were 2,455 cases of occupational skin disease in 2009 reported by dermatologists and occupational physicians reporting in the THOR (EPIDERM and OPRA) network.

In the USA OSHA reports that in 2006, 41,400 recordable skin diseases were reported by the Bureau of Labor Statistics (BLS) at a rate of 4.5 injuries per 10,000 employees, compared to 17,700 respiratory illnesses with a rate of 1.9 illnesses per 10,000 employees.

So direct effects on the skin is clearly a significant problem in industry (and these statistics probably underestimate the extent of skin problems).

It is much more difficult to determine the extent of problems due to skin absorption. Many industrial organic solvents and some other less common substances can be absorbed through the skin. It’s not always easy to identify them. EH40, HSE’s list of Workplace Exposure Limits and the ACGIH Threshold Limit Values include “SK notations” which are applied to substances where skin absorption can make a substantial contribution to body burden. In addition,not all substances in EH40 and the TLV list than can pass through intact skin have been assigned Sk notations, and WELs and TLVs have only been applied to a small proportion of substances encountered in the workplace. However, there is a good chance that any solvent that can affect the skin can also be absorbed.

So skin contact is something that needs to be properly considered during COSHH assessments. Evaluating the degree of risk isn’t easy – particularly with skin absorption where there isn’t a good universal method available for quantifying absorption. However, COSHH is about controlling risks – the  assessment is not an end in itself but the means of deciding which risks need to be controlled. So  where skin contact occurs the best approach is to identify suitable controls.

Unfortunately, in my experience, the usual response by employers is to issue personal protection such as gloves or protective clothing. (And, the HSE’s own  COSHH Essentials takes this approach). PPE should only be used as a last resort. The COSHH Regulations themselves  specify that it should only be used “where adequate control of exposure cannot be achieved by other means”. This doesn’t only apply to respiratory protection.

Where chemical protective gloves and clothing are used, they rarely provide effective protection other for short duration tasks. Yet employers and workers often have a misguided belief in their effectiveness which can actually increase the risk to health. The best approach is to look to change the working method so that skin contact doesn’t occur, or is a least minimised to the lowest level practicable, or to find a suitable engineering control. Appropriate gloves can then be worn as a secondary control.


Picture credits:

HSE Work-related skin disease image library

Preventing dermatitis at work. Advice for employers and employees

Heat stress indices


Assessing the risk from the thermal environment is not easy. One of the main reasons for this is that there are a large number of factors which affect our physiological response to heat. The main ones are

Four environmental parameters

  • Air temperature
  • Mean radiant temperature
  • Relative humidity
  • Air velocity

And three “human” factors

  • Work rate (which affects metabolic rate) and
  • Clothing level
  • Whether the person is acclimatised to hot conditions

thermal env

All of these parameters* can be quantified, either by measurement or estimation, but it is very difficult to make sense of the results. We need to find a way of pulling them together so we can decide whether we have a problem and, if so, how big the problem is.

Over thirty different indices have been developed over the years, taking into account some or all of these parameters, which aim to integrate the relevant variables into a single value which relates to the stress placed upon workers by the thermal environment they encounter. These indices have differing degrees of success in meeting the objective of a single number descriptor for any situation. Each has a range of environmental parameters over which it is applicable, but outside of this range accuracy is questionable.

A number of these indices are listed in the syllabus for the BOHS Occupational Hygiene Module M201 “Thermal environment and non-ionising radiation (including lighting)”:

  • Effective Temperature (ET)
  • Corrected Effective Temperature (CET),
  • Wet Bulb Globe Temperature (WBGT),
  • Heat Stress Index (HSI) and
  • Predicted 4- Hour Sweat Rate  (P4SR)

Although they have to be covered during the course, these indices, except for WBGT, are out of date and, in practice, are no longer used (although ET is still applied in the mining industry in the UK and some other countries). In the main, they are of historical interest only.

The relevant indices for modern practice are WBGT and the more complex “Predicted Heat Stress” (PHS) index described in International Standard ISO 7933:2004 “Ergonomics of the thermal environment – Analytical determination and interpretation of heat stress using calculation of the predicted heat strain”. The latter is not mentioned in the current BOHS syllabus.

WBGT is easy to use and apply. The threshold limit values (TLVs) established by the American Conference of Governmental Industrial Hygienists (ACGIH) use the WBGT index. The TLVs also incorporate guidance on how to assess the risks from heat stress and strain, which include screening criteria based on the WBGT index and basic advice on  controls including work:rest regimen for different situations

PHS is extremely complex and intended to be used by experienced ergonomists or occupational hygienists.  The index determines a duration limited exposure time, which is the time taken for either the rectal temperature or the cumulative water loss reaches specified maximum values. The lower of the two values is used to determine the allowable exposure time. Solving the PHS equations requires the use of a computer program and should only be attempted by someone with appropriate experience.

In practice, for situations where there is a potential risk from heat stress and strain, it is best to adopt a structured approach.

  1. Undertake screening using a simple method that can be used by management and workers to identify potential risks from heat stress and strain and determine whether further work is needed. The HSE have a useful checklist that can be used during a screening survey that can be downloaded from their website.  Following the survey if it is clear that there is no risk no further action will be required. Also, if there are obvious problems it may be possible to specify appropriate controls at this stage. The HSE checklist can help with this.
  2. If the risk cannot be adequately assessed during stage 1, carry out a basic analysis taking appropriate measurements and interpreting them using WBGT. In many cases it will be possible to use the guidance provided in the ACGIH TLV for heat stress to determine whether the risk is significant and what controls and other measures could be implemented.
  3. For very complex cases, where it is not possible to adequately evaluate the risk during the previous two stages, commission an expert analysis which is likely to involve measurements/estimates of physical and/or physiological parameters and use of more complex indices.


* Other factors can also influence the risk too, such as posture, body weight, medication. A fully comprehensive analysis would consider them too, although it is not so easy to quantify them and including them introduces complications.

Diesel exhaust emissions – what to measure?

fork truck

We recently had a query from a client who’d had a visit from their local Factory Inspector. The client has a large warehouse where they operate diesel powered fork lift trucks. The Inspector asked about the client about their risk assessment of the emissions and then suggested that they arrange to measure the emissions.

Diesel exhaust emissions are a complex mixture of gases and particulate matter. Major components include :

  • carbon;
  • nitrogen;
  • water;
  • carbon monoxide;
  • aldehydes;
  • nitrogen dioxide;
  • sulphur dioxide;
  • polycyclic aromatic hydrocarbons (PAHs).

Quite a number of these contaminants are irritant gases, that can affect the eyes and respiratory system. There are also concerns about the potential risk of cancer from inhaling this complex mixture. Some studies have shown a small increase in lung cancer for people exposed to diesel exhaust emissions and the International Agency for Research into Cancer (IARC) have concluded that diesel engine exhaust is probably carcinogenic to humans. This may be due to the presence of PAHs in the emissions.  Another consideration is that, due to the way it is formed, the particlulate matter is nano-sized, and can be absorbed through the lungs and transported around the body. There are concerns that nano-particles may cause adverse effects on the heart and cardiovascular system

Although a number of the individual components have Workplace Exposure Limits (WELs), and can be measured fairly easily, simply quantifying each substance does not give an adequate evaluation of the risk, particularly as there could be additive or more complex interactions. In any case, some of the components presenting the greatest concerns (nano-particles, PAHs) do not have WELs.

So although some components can be measured, it’s not so easy to interpret the results.  In such cases it is best to remember the real objective of risk assessments – i.e. to determine what controls are required. The HSE have published some guidance in their publication Control of diesel engine exhaust emissions in the workplace (HSG187). It is usually obvious when there is a significant problem with the emissions from diesel engines. If visible black smoke is pouring out of the exhaust pipe something needs to be done! It’s not always so obvious, but the UK Health and Safety Executive (HSE) have developed some guidelines based on observations, subjective assessment of irritancy and measurement of carbon dioxide levels, which give an indication of whether control is adequate.

Table 1 – Guidelines for the assessment of the level of exposure to DEEEs – From HSG 187


Carbon dioxide can be measured easily using a simple colorimetric indicator tube. But note that in this instance it isn’t appropriate to compare the results with the WEL for the gas – it is being used as an “marker” of the overall emissions and standard of control.

It’s quite possible to measure the particulates, but the analysis is very expensive and there isn’t a WEL. Without a standard against which the results can be compared, measurement results don’t help us to decide on the degree of risk and whether improved controls are needed. In this case, particulate sampling is an expensive exercise which doesn’t help us to draw useful conclusions. Using a pragmatic approach of observations and simple measurements of marker compounds is the most cost effective way of assessing the risk and deciding on what controls are needed.

The following provide some further information on the assessment and control of diesel engine exhaust emissions:

Health and Safety Executive – indg286 Diesel Engine Exhaust Emissions

Health and Safety Executive Control of diesel engine exhaust emissions in the workplace (HSG187)

Rogers and Davies Diesel Particulates—Recent Progress on an Old Issue The Annals of Occupational Hygiene 2005 Volume49, Issue6 Pp. 453-456

Diesel Engine Exhaust – California Department of Health Services

Photo credit: Stock:xchng