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Control of risks to health from work 


Note: This page is not intended to be a comprehensive or exhaustive occupational hygiene account of health hazards, risks and means of risk reduction in this particular type of workplace, but is intended to exemplify aspects of the Management of Health and Safety in Workplaces and to assist in education and practical implementation about this.
The responsibilities of the employer mainly stem from legislation such as the Health and Safety at Work etc. Act (1974) but other recent UK and European Union legislation is very important in managing Health and Safety at work. These include the Management of Health and Safety at Work Regulations, Control of Substances Hazardous to health Regulations, Manual Handling Operations Regulations,Personal Protective Equipment at Work Regulations, and various others. 

View the image (left) which shows a worker, following appropriate work practice, protected from a chemical exposure contained within a reaction vessel, provided with local exhaust ventilation at the orifice of the vessel, designed so as to suck away any gases or vapours as they emanate from the vessel. In addition, he is wearing personal protective equipment consisting of an airhood supplied by piped breathing air, as well as rubber gloves, safety shoes and other skin protection. In his case there are therefore several lines of defence to protect him from exposure. 

Another resource using the same photograph but with mapping in relation to a dynamically variable caption is also available

You can read in more detail about the principles and concepts of control of risks to health at work as well as about further examples below. 

worker with protection


None of these methods is flawless and several should normally be used in combination. The following will give a brief account of each, and will invite you to think of problems with each of them. 


1. Elimination of hazards 

e.g. closing down unacceptably unsafe plant/machinery, perhaps even by a prohibition notice. 

Noise injury may be prevented by specification in the design of new machinery. 

Substitution of hazards 

e.g. substitution of benzene by cyclohexane or by toluene, or of asbestos by man made mineral fibre (MMMF), or substitution or of white-spirit based paints by water based emulsions. 

Do these steps abolish the risk? 

The widespread substitution of solvents such as toluene and white spirit for benzene which can cause leukaemia has given rise to the concept of 'safe' solvents. However these substances are only relatively safe, and their uncontrolled use may lead to neurological or psychological disease. Similarly, certain fibrous minerals used as substitutes for asbestos may themselves have carcinogenic potential, and require careful handling. 

2. Enclosure/Segregation so as to reduce exposure 

e.g. to reduce exposure to fume or vapour, noise or heat e.g by Segregation of workers from the source of harm. This may be by time or distance, as in mining where workers retire to a safe distance at the time of blasting, and when such operations take place on shifts when fewer workers are about. More commonly, however, it involves enclosure of the process so that there is a physical barrier between the source of harm and the workers. 

Can segregation work for all workers? 

Unfortunately not - those involved in maintenance for example can be at particularly high risk. A case has been described in which an organic dye process was properly enclosed, but fitters required access for maintenance and repair. One of these men subsequently developed bladder cancer. Similarly, in a very clean and well-kept bakery the only man who developed asthma due to flour allergy was the fitter who had to repair pipes and silos when they burst. Remember, when looking at a well isolated piece of machinery, to ask how it is maintained or repaired. 

3. Local exhaust ventilation etc

Local exhaust ventilation is used where the above methods are impracticable. Ideally it is combined with partial enclosure of the process, as in the familiar fume cabinet. Alternatively, the ventilation is applied very close to the point of generation of the dust or vapour if appropriate to remove fume or vapour at source e.g. in soldering. The air velocity required to draw the substance away is called the capture velocity, and this depends on the physical characteristics of the substance and the mechanisms of its release. It is intuitively obvious that lower velocities are needed to clear evaporating chemicals than particles generated by blasting or drilling. 

What problems could you think of, in relation to local exhaust ventilation? 

This is very effective if properly designed and if the extractor fan is working. A young female technician developed allergic alveolitis and asthma due to sensitization to a chemical reagent she was preparing in a fume cupboard in the laboratory of a university medical school. When the problem was investigated, it was found the extractor fan was not working. Three men developed acute mercury poisoning while making repairs in the boiler of a power station. Some other workers in a distant part of the plant had spilt some mercury which had vaporised. The extract fan in the system was running in reverse and the vapour was propelled along pipes to the boiler in which the other men were working. 

Reduction of airborne levels of substances may also be achieved by dilution ventilation or precipitation. A familiar example is the use of water and high air flows in mines to reduce dust levels. 

Does dilution ventilation abolish the risk? 

The substance remains in the air, but in lower concentration. Unforeseen problems may however occur to make matters worse. In some cases, the supply of conditioned, humidified air to workplaces has resulted in new problems e.g. from infection, allergy or other effects, e.g. in operating theatres it has resulted in humidifier fever among theatre staff. 

Electrostatic forces may also be used to reduce levels of dust, commonly in preventing pollution by smoke stacks. 

4. Appropriate education, work organisation and practice 

Education as well as good housekeeping remain important principles of prevention in all circumstances. Workers should be made aware of dangers by instruction, notices, codes of practice and safety audit. Similarly, managers should be trained in their responsibilities in these respects. Good housekeeping, keeping chemicals in safe places, not leaving dangerous materials (or indeed any materials) lying about, making sure that everything is clearly labelled, vacuuming floors and benches after use, and other such measures will reduce risks of illness and accident and will ensure that everyone is safety-conscious. 

Other examples include implementation of policies on safe working practice, regulated hours of work and careful planning of shiftwork 

5. Personal protection 

The law generally requires all reasonable efforts be made to engineer the hazard out or to shield individuals from it. Only then is it permissible to resort to personal protection. Most such devices are not comfortable for long-term use and give only partial protection. Included in this category are respirators, protective clothing and gloves, eye shields and hearing defenders. Clearly in some circumstances they are mandatory - eye protection in welding and metal work, ear muffs in caulking (which today means hammering metal in ships' hulls), and so on. However, they should never be relied upon as the sole, albeit cheap, method of protecting workers. Where they are used, care should be taken in their design, in terms of comfort and wearability, as well as in their efficiency in terms of protection. 


  • gloves, 
  • goggles, 
  • masks,
  • protective steel toe capped footwear
A good account is available from CCOHS OSH-Answers

What problems in relation to personal protective devices can you think of? 

Sometimes personal protection devices may perform significantly worse than implied by their 'nominal protection factor'. Face masks are not as universal in their fitting to the human face as manufacturers and wearers would hope, and thus often allow leakage. Filters on respirators need changing regularly or their performance deteriorates. Some disposable respirators become ineffective after use because of being crumpled in a pocket or soaked with water. Respirators require to be formally tested to various standards - in doing this, testing laboratories have found filters that release respirable fibres, giving higher counts within the masks than outside! Some helmet type respirators become less efficient if used in moderately windy conditions. Ear plugs may contribute to infection in the outer ear (otitis externa), visors may obscure the welding job and thus not be used properly, gloves may be permeable to chemicals, and so on. The correct personal protection must be chosen. The following image shows the hands of a worker who had been provided with high quality thick black rubber gloves as personal protection. These would probably have been suitable to protect her from caustics. Unfortunately they were the wrong sort to protect her from the alkylating agent that she was handling. The blistering on her right hand was the consequence of  the wrong protective measures: 

Acknowledgement: Part of this page has been adapted, with permission, from Practical Occupational Medicine (Copyright) - Arnold publishers.

A Diploma and a MSc course in Occupational Hygiene are available at the University of Manchester