28th October, 2021

Risk Measurement Explained In Health And Safety

When you carry out a risk assessment, you need to measure risks. Are the risks involved high, medium or low? But how do you measure the risk level? In this blog, we explain how to break down the measurement and rating of risks for health and safety.

Risk Measurement Explained In Health And Safety header image

There can be risks in all aspects of our lives. Risk of failure. Risk of loss. Risk of missed opportunities. Risk of harm.

And that last item, the risk of harm to ourselves and others, is at the core of health and safety. To measure the risk and eliminate or reduce that risk as low as is reasonably practicable (ALARP).

But most risk assessments are qualitative. They rely on the personal judgement and expertise of the assessor. The assessor uses their own experience and consults with others carrying out the activity and best practice guidance to reach their decisions.

When health and safety risk measurement is based on judgements and opinions, it's not always easy to see how the decisions were reached. Or find a formula to follow. So in the post, we're going to break down risk, and how you can measure it.

What is a health and safety risk?

Part of the legal duty to carry out risk assessments includes identifying the hazards involved in an activity and deciding what to do about them.

Having identified the hazards, you then have to decide how likely it is that harm will occur, ie the level of risk and what to do about it.

Step 2 of the five steps to risk assessment is to decide who might be harmed and how. And as you will find out in this blog post, that's all about measuring risk. So what is a health and safety risk?

A health and safety risk is the chance that somebody could get harmed by a hazard.

You can't describe a risk well without measuring it. You could say, "working at height is a risk", but that doesn't tell you anything. What is the risk? What would you need to know about the risk? Well, first, you need to know how serious the harm could be. And second, you need to know how likely it is for the harm to happen.

Hazards and risks are often confused with each other, but they are not the same. Find out more in the difference between hazard and risk explained.

How do you measure risk?

Risk = Likelihood x Severity.

Let's go back to our definition of risk. A health and safety risk is the chance (likelihood) that somebody could get harmed (severity) by a hazard.

It's important to consider both likelihood and severity when measuring health and safety risks. A common mistake could be to think, how likely is it that someone could be harmed?

But imagine if you had two risks, and they both had the same high chance that harm would occur. The risk level for both would be high if you only consider the chance (or likelihood) of the harm occurring. But what if in one the harm was dry skin, and in the other the harm was fatal. Are both these risks the same?

If you only consider the chance of the harm occurring when calculating the risk level, you would consider both of those examples as high risk. But really, only one is. That's why when assessing risk, you need to consider both the likelihood (the chance) and the severity (the type of harm).

And back to our earlier example of "working at height is a risk". Now we know the formula for measuring risk, we can provide more information about the risk.

If there was no barrier, the risk could be "someone could easily fall (likelihood) and the fall could kill them (severity)". Now you know the risk and can do something about it.

Once you measure risk, you need to control it. Find out more in the hierarchy of risk control.

If risk = likelihood x severity, then you need to know what the likelihood and severity levels are to get the risk. How do you do that? Accident statistics and industry guidance can help you. But, often, this is going to rely on some personal judgement and experience.

You can also use a risk matrix and clearly defined scales to help structure your risk measurements and calculations. Let's look at how we can break down likelihood and severity, so you can most accurately measure health and safety risks.

Measuring Likelihood

The chance is the likelihood. How likely is it that the harm will occur? In a simple 3x3 risk matrix, you might break this down to:

  1. Rare
  2. Occasional
  3. Frequent

Or you break this down even further (as we do in the free risk assessment calculator) to:

  1. Impossible
  2. Remote
  3. Unlikely
  4. Possible
  5. Unusual
  6. Known
  7. Likely
  8. Usual
  9. Certain

The higher up the scale, the more likely it is for harm to occur.

And remember, putting in place controls will reduce the likelihood. While it's almost certain someone would fall from a platform with no edge protection, with suitable barriers, it becomes unlikely.

Measuring Severity

Just like with likelihood, we can break down severity into a simple 3x3 risk matrix:

  1. Slight Harm
  2. Moderate Harm
  3. Extreme Harm

And you can also break down severity even further (as we do in the free risk assessment calculator) to:

  1. Insignificant
  2. Minor Incident
  3. Minor Injury
  4. Health Damage
  5. Injury
  6. Multiple Injuries
  7. Serious Injury
  8. Fatal
  9. Multiple Fatalities

The higher up the scale you are, the more severe the harm is.

And, just like likelihood, you can reduce the severity with suitable control measures. Going back to our falls from height example, a fall from a height would probably be serious or fatal. But if the people at height wore a harness, or a safety net was installed, you could reduce the consequences of a fall to a minor incident.

Risk = Likelihood x Severity

Now you have the likelihood and severity, you can finally measure the risk. And this is where assigning numbers, like in a risk matrix, can help you, especially when it comes to knowing if risks are high, medium or low.

5x5 risk matrix

The higher the likelihood, the higher the number. The higher the severity, the higher the number. So, when you multiple two high numbers together, you get an even higher number! Multiplying the number assigned to likelihood with the number assigned to severity is a good way of rating your risk levels. The higher the number, the higher the risk.

You don't have to assign numbers, and there's no requirement to do so. A simple matrix will work without numbers too.

Slight Moderate Extreme
Low Very Low Risk Low Risk Medium Risk
Medium Low Risk Medium Risk High Risk
High Medium Risk High Risk Intolerable Risk

Once you know the risk level you are dealing with, you can think about the control measures you need. Remember, risk must be reduced as low as reasonably practicable.

If you need help calculating risk, use the free risk assessment calculator to get your risks in order.

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This article was written by Emma at HASpod. Emma has over 10 years experience in health and safety and BSc (Hons) Construction Management. She is NEBOSH qualified and Tech IOSH.

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