Defining Risk

August 2022

In the risk assessments we audit we sometimes see confusion over the terms used to describe risk.  In the 2021 LCA Legionella Risk Assessment service delivery standard and in BS8580-1:2019 the terms Inherent, Residual and as low as reasonably practicable (ALARP) are used. The following is intended to help clarify the terms.

Inherent Risk
This is the underlying risk if there were no controls in place, or if controls were to fail or be removed.  
For example, a hot and cold water system with storage tanks and large calorifiers is a higher inherent risk than a mains fed system with a point of use instant heater.  Some systems will generally always be higher inherent risk as they rely on water treatment for control; for example, cooling towers or spa pools.

The inherent risk is something that the risk assessor needs to quantify, and it may be possible to make recommendations to reduce the inherent risk with changes to the system.  The hierarchy of control outlined in COSHH starts here with elimination or substitution of risk.  For example, removing a cold water storage tank and converting to mains feed will reduce the inherent risk presented by the water system.
Residual Risk
This is the risk observed by the assessor during the risk assessment process with the current controls in place.  Residual risk can be reduced with additional controls or by reducing the underlying inherent risk as above.  For example, the residual risk of a hot water system running at 40oC is high and this can be reduced by applying the control measure of increasing the hot water temperature to store at 60oC and distribute above 50oC.
As low as reasonably practicable risk is a judgement for the risk assessor to make, often in consultation with the responsible person.  ALARP is the target to reach and the recommendations in the risk assessment must bridge between where the risk is now, and the ALARP risk level.
It is important for risk assessors not to make impossible or impracticable recommendations in their risk assessments.  Cost, however, is not an overriding factor on all levels of practicability.  While it may not be possible to reach a level of ‘no risk’, the acceptable level of risk is ALARP.  The HSE define and describe ALARP as follows:

The definition set out by the Court of Appeal (in its judgment in Edwards v. National Coal Board, [1949] 1 All ER 743) is:
“’Reasonably practicable’ is a narrower term than ‘physically possible’ … a computation must be made by the owner in which the quantum of risk is placed on one scale and the sacrifice involved in the measures necessary for averting the risk (whether in money, time or trouble) is placed in the other, and that, if it be shown that there is a gross disproportion between them – the risk being insignificant in relation to the sacrifice – the defendants discharge the onus on them.”
In essence, making sure a risk has been reduced ALARP is about weighing the risk against the sacrifice needed to further reduce it. The decision is weighted in favour of health and safety because the presumption is that the duty-holder should implement the risk reduction measure. To avoid having to make this sacrifice, the duty-holder must be able to show that it would be grossly disproportionate to the benefits of risk reduction that would be achieved. Thus, the process is not one of balancing the costs and benefits of measures but, rather, of adopting measures except where they are ruled out because they involve grossly disproportionate sacrifices. Extreme examples might be:

    • To spend £1m to prevent five staff suffering bruised knees is obviously grossly disproportionate; but
    • To spend £1m to prevent a major explosion capable of killing 150 people is obviously proportionate.

Of course, in reality many decisions about risk and the controls that achieve ALARP are not so obvious. Factors come into play such as ongoing costs set against remote chances of one-off events, or daily expense and supervision time required to ensure that, for example, employees wear ear defenders set against a chance of developing hearing loss at some time in the future. It requires judgment. There is no simple formula for computing what is ALARP.
Reassessment Frequency
When recommending a risk assessment reassessment frequency, the assessor must make a judgement on how long could reasonably be left between reassessments, should nothing trigger a reactive review.  The inherent and residual risk should be considered when determining this frequency.  A high inherent or residual risk system might need to be reassessed annually or sooner.  A low inherent risk system might warrant a backstop reassessment frequency of several years.