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.