Going Underground–In Liverpool

Last week The British Occupational Hygiene Society held a joint conference with the Occupational Hygiene Society of Ireland (OHSI) in Liverpool. Exposure Control and Containment 2 (ECCII), was a follow up to the successful event held in Cork two years ago. The Conference was held in the Crowne Plaza Hotel on the waterfront, just a short distance from the “Three Graces” at the Pierhead.

During the afternoon of the first day of the conference delegates were given the opportunity of joining a site visit. This entailed a short walk to this building, located in George’s Dock, just behind the Mersey Docks and Harbour building.


A large Art Deco style structure faced with Portland limestone and decorated with Egyptian motifs that were popular in the 1930’s, not long after the discovery of the tomb of Tutankhamen. It’s effectively a huge chimney surrounded by offices built as part of the ventilation system for the Queensway Tunnel (also known as the Birkenhead Tunnel). It’s certainly one of the fanciest chimneys I’ve ever seen!

It was designed by Liverpool architect Herbert James Rowse (1887-1963) and the carved Egyptian style decorations on the portals are by sculptor Edmund Charles Thompson (1898-1961).


The control centre for the tunnel ventilation system, as well as one of the ventilation stations, is located here and this is what we went to visit.

The tunnel was opened in July 1934, and at the time, at 3.24 kilometres (2.01 mi) long.  it was the longest road tunnel in the world, a title it held for 14 years until the opening of the Vielha Tunnel in Spain in 1948. It remained the longest underwater tunnel though, until 1955. The entrance is right in the centre of Liverpool and being built in the 1930’s it only has a single carriageway of four lanes, two in each direction.

Mersey Travel, who own the tunnel, organise regular tours of the tunnel showcasing its history and allowing the public to gain access to the old control room, ventilation equipment and the tunnel itself. They also can arrange special tours for schools, companies and other organisations. Given the theme of the conference – about the control of exposure to hazardous substances – the tour was customised to highlight how the air quality is controlled.

After donning our hi-viz vests and safety helmets, our guides, Alison and Billy, gave us a potted history of the tunnel and described how it was constructed. Billy was a real “Scouser” – born and bred in Anfield (although a true Evertonian!) with lots of stories and plenty of jokes and wisecracks. A true entertainer!


The tunnel cost £8million to build  and employed 1700 men in difficult working conditions under the river bed. 1,200,000 tons of rock and gravel had to be excavated by two teams working from either side of the river. Pilot tunnels were excavated, one starting in Liverpool and the other in Birkenhead, eventually to meet in the centre – less than an inch out of alignment! – on 3 April 1928. The pilot tunnels were then enlarged to create the full sized tunnel.  There’s more information about its construction on the Merseyside Maritime Museum Website and a more detailed description here.

First stop was the old control room, which was in use until relatively recently. This required climbing several flights of steps (you need to be fit for this visit!!)


2016-10-12 13.31.07


Ventilation of the tunnel to remove contaminants from vehicle exhausts, is provided by massive fans located at 6 ventilation stations, including the one at George’s Dock. Fresh air, brought in from above street level, is blown through the ducts beneath the roadway. The air enters the upper half of the tunnel through outlets18 inches apart at roadway level. The air flow is balanced by varying the size of the outlets to ensure an even distribution of air throughout the tunnel. Contaminated air is extracted through vents in the roof of the tunnel to the exhaust chambers at each of the six ventilating stations.

It’s incredible to think that the original fans, built and installed in the 1930’s, are still in use. They are enormous, with the largest capable of moving 641,000 cubic feet per minute (315 cubic metres per second).


I was rather pleased to hear that one of the two fan suppliers was Walker Brothers of Wigan (my home town) who specialised in equipment for mines. In the 1930’s there was little knowledge or experience of how to control air quality in road tunnels so, perhaps not surprisingly, they fell back on the technology used to ventilate coal mines.

Here’s some old pictures showing the fans being installed.

Fan in the Queensway Tunnel on Merseyside


This diagram illustrates the operation of the ventilation system (showing the Birkenhead side). It appeared in the second edition of a short lived British magazine “Wonders of World Engineering”,  published in March 1937.


I found the image here.


We were then taken all the way back down and below ground level to look inside the tunnel itself. It’s very narrow and the cars speeded past only centimetres from where we stood on the observation platform. No photographs were allowed to minimise the distraction of drivers of the vehicles passing through the tunnel – we didn’t want to be the cause of an accident.

Then it was back up the stairs to the ground floor where we handed in our safety gear at the end of what was a very informative and entertaining visit.


Health and Safety in Engineering

On Tuesday this week I went down to London to represent BOHS at a reception in the House of Commons held to launch a new document on the business case for health and safety in engineering. It was produced by the Inter-Institutional Group on Health and Safety, an organisation made up of representatives from the engineering professional bodies.

The document highlights the essential and growing role of engineering in supporting health and safety risk management and economic sustainability, listing some key steps for engineers, managers and government to consider. The business case for health and safety engineering solutions is outlined, providing real-life examples of many engineering-related successes and failures, supported by an explanation of how and why the case needs to be made more strongly. The examples are largely safety related, particularly focussing on major construction projects, but there is mention of occupational health.

The need for health and safety to be considered early in an engineering project is stressed and that really is key. It’s usually much easier to incorporate effective controls at the design stage. Retrofitting engineering controls such as containment and local extraction is not always easy and often results in ineffective design and use of “off the shelf” solutions which may not be appropriate to the nature of the risk.

A multidisciplinary approach is recommended with project engineers involving health and safety specialists, including occupational hygienists, at the design stage and throughtout the project. Working togethor problems can be identified and resolved at an early stage.

It’s good to see engineers taking health and safety seriously. Hopefully the document will be widely circulated and the principles it advocates implemented, reducing accidents and injuries and preventing ill health.

Design and management of controls

I’ll be making a contribution to the BOHS Conference in Cardiff this year, first thing on the Thursday morning, titled Managing the Design and Implementation of Controls – A Review

The usual definition Occupational hygiene is that it is :

the discipline of anticipating, recognising, evaluating and controlling health hazards in the working environment with the objective of protecting worker health and well-being and safeguarding the community at large.’ (Source : International Occupational Hygiene Association)

Recognition and evaluation are important steps but, for me, they’re a means to an end, not an end in themselves. As occupational hygienists our priority has to be control. The other steps should really be about providing us with information to help us to make decisions on minimising risks to health.


Unfortunately, controls are often badly designed and implemented, meaning that they are of limited effectiveness. There are a number of reasons for this, but, in my experience, ineffective control of exposure often occurs due to failures in the management process. If employers are to improve on this they need guidance. And occupational hygienists and other H & S professionals need to be able to analyse problems to help management avoid and overcome them.


My talk will outline a management framework that sets out the key steps for the effective specification, design and implementation of control measures. I’ll be including a number of case studies showing how the framework can be used to analyse and identify problems.

Inevitably, I only have limited time and can only provide a brief introduction to the framework, so I’ve produced a Slideshare presentation that provides some additional background and more details.

Controlling silica exposure during fettling of castings

In foundries, once  the casting is removed from the mould it is usually necessary to remove excess metal and remedy defects. This process is usually referred to as “fettling” or “finishing”.


Fettling normally involves the use of powered hand tools such as chippers and grinders. The operation presents a number of significant risks. Using power tools exposes the workers to high noise levels and hand-arm vibration. There is also a risk from exposure to the dust generated by the process. The dust will largely consist of metal particles, but this is usually of low toxicity. The main concern occurs where sand is used for the moulds in which the metal is cast. This is crystalline silica. Some particles of sand from the mould adhere to the metal and grinding during fettling can lead to the release of fine dust including particles of respirable crystalline silica. “Respirable”  particles are smaller than 10 microns in diameter and can reach the deepest regions of the lung. Regular, repeated exposure to respirable crystalline silica can lead to silicosis, a serious, debilitating lung disease.


Risk of silicosis – Source: HSL

Respirable crystalline silica has a very low Workplace Exposure Limit of 0.1 mg/m3 as respirable dust. In fact, as the above chart shows, long term exposures to concentrations much lower than this can lead to some workers developing silicosis. There is also evidence that prolonged workplace exposure to crystalline silica can lead to an increased risk of lung cancer, although this is only likely to occur in those workers who have already developed silicosis. Given the nature of the risk exposures need to be reduced as low as practicable.

So, it’s important to ensure that the dust generated during fettling is properly controlled, particularly when there is a risk of exposure to silica. In most cases, the most practical and effective way of doing this is to install well designed local exhaust ventilation. The Health and Safety Executive have developed a number of sheets providing practical advice on how to control dust and fume generated during foundry processes, including fettling. For small castings they recommend the installation of an extracted booth. The work is carried out inside the booth which then contains the dust generated allowing it to be removed effectively by the extraction.


Source: HSE COSHH Essentials for foundries. FD7 “Fettling small castings”

Recently, one of our consultants was carrying out a survey in a foundry. They had installed this type of booth for their fettling operations. However, as can be seen in the following photograph,  The booth was not being used in the way intended – the worker was carrying out the work outside the booth.


The dust generated was not contained and, consequently, the extraction would not be as effective as it should be. The worker will have a higher exposure than if he carried out the fettling inside the booth.

In a previous post I outlined the key steps needed to control health hazards in the workplace. The first steps are recognising that a risk exists and then making sure that appropriate, effective controls are specified, designed and implemented. In this case the risk from dust exposure was recognised and a local exhaust ventilation system with an appropriate hood design was installed. The problem is that it is not being used properly, considerably reducing its effectiveness.

Once controls have been implemented they need to be properly managed to ensure that during use they continue to do the job they were designed to do. This requires training, supervision, maintenance, testing, audit and review. It’s a management responsibility to ensure that controls are properly used so more vigilant supervision seems to be required.

In this example, there could be a number of possible reasons why the booth was not being used correctly. Perhaps management and the workforce don’t fully understand the health risks and so don’t appreciate the importance of using the controls properly. Perhaps the workers haven’t been properly trained on how to use the booth. However, there could be a problem with the design of the booth. It is possible that carrying out the work inside the enclosure presents the operator with some practical difficulties. Perhaps the fine work required is difficult to complete properly if the casting is inside the booth or the booth dimensions, particularly the height, could cause the worker to adopt an awkward posture which causes discomfort and could lead to musculoskeletal problems. Solving one problem often creates another. Ergonomics is often neglected when designing engineering controls for chemical hazards. Ideally workers need to be consulted and involved in the specification and design of the controls and its good practice to build and test a prototype before finalising the design. Proper commissioning of the controls should also check for usability.

Further investigation would be required to get to the root cause of this problem. However, the case illustrates the importance of proper management of the design, implementation and use of controls.

Key steps to control health hazards

At the end of June I was invited to make a presentation to the BOHS workshop on the control of health hazards at work. The key points made are summarised in a previous post.

I’ve finally got round to uploading the slides I used to Slideshare. These days I try not to overload my presentations with bullet points to avoid the risk of “death by Powerpoint” so I’ve added some explanatory text on the individual slides for the Slideshare version.

Reconsidering the “hierarchy of control”– Part 2

In a recent post I discussed the basis of the hierarchy of control and how it should be applied in practice. It’s something we cover when we deliver the BOHS module M103 “Controlling hazardous substances” and is also relevant to the control of physical hazards such as noise and vibration.

During the M103 course I’ll normally include an exercise where I ask the participants to list the different types of controls they’d include in the main categories (i.e. source, path and worker). They will usually include “training” in the list of worker based controls. Now, I’m not one for being controversial(!) but I usually use this as an opportunity to start a discussion as I don’t think training fits here. “Training” is something of a vague term. Of itself it won’t control exposure.


When we talk about training as a control what we are usually thinking about is the underlying measure – good working practices or safe working procedures. Different ways of carrying out a job can lead to different levels of exposure. To minimise the health risks we need to establish which working practices will minimise exposure and make sure workers are aware of them. Training will help with this, but only if we’ve identified the best methods. Training workers in poor methods will actually be counterproductive and increase exposure.

In fact training (along with information and instruction) is always needed whatever controls are introduced. Workers need to be aware of the hazards they’re working with and the associated risks. They also need to know why they shouldn’t reintroduce a substance that has been eliminated or substituted, how to use any engineering controls provided properly and, where appropriate how to maintain and test them, what good working methods and safe working practices need to be followed and how to obtain, fit, use and maintain personal protective equipment. In fact quite a lot of training is needed in most cases. So, although I don’t “training” fits into the traditional list of measures in the hierarchy, it’s an essential component of an effective control regime.

To me, training fits into a group of measures that are usually needed to ensure that the controls that have been introduced continue to work effectively. I call these the management measures  and they sit alongside the traditional hierarchy of control.

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. They include

  • information, instruction and training to ensure workers know why the controls are needed, how to use them correctly, procedures for reporting faults etc.
  • supervision to ensure that the controls are used properly
  • maintenance and testing to ensure that engineering controls and personal protective equipment continue to operate effectively
  • auditing to ensure that the procedures and safe working methods are followed
  • exposure monitoring and health surveillance as additional checks that the controls are effective
  • welfare facilities (i.e. washing facilities, changing rooms, segregated rest rooms, separate storage for clean and contaminated clothing) may need to be provided.
  • good housekeeping and cleaning of the workplace.

Anyone familiar with the British Control of Substances Hazardous to Health Regulations (COSHH) will recognise them, as they form the basis of regulations 8 to 13

We can modify the “hierarchy of control” model to incorporate them as illustrated in the following diagram. The management measures form a separate list running in parallel with the traditional list of controls.


Once appropriate prevention strategies, engineering measures, work practices and PPE have been identified, employers need to decide which of the management measures should be introduced as part of a control regime to ensure that the controls continue to work effectively at reducing the risk to an acceptable level.

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.