A hazard is anything with the potential to cause harm. A risk is the chance that somebody will be harmed by it, together with how serious that harm could be. The distinction sounds academic until you write a risk assessment, at which point it decides whether the document is any use: a page listing hazards with no evaluation of risk is a list of things that exist, not an assessment.
Hazard definition in safety, in plain terms
A ladder is a hazard. So is a drum of solvent, a wet floor, a noisy machine, a deadline that has people working tired, and a member of the public walking past an open excavation. The word carries no judgement about how likely harm is. It is a property of the thing or the situation, and it is there whether or not anybody is exposed to it.
Hazard and risk: why risk needs two numbers
Risk combines likelihood and severity. A hazard that could kill but that nobody can reach is a low risk. A hazard that will only ever cause a bruise but that fifty people meet every day may be a higher one. Assessments that score only severity end up treating every chemical as an emergency, and assessments that score only likelihood miss the rare thing that kills.
Types of hazard you are expected to have thought about
The usual grouping is physical, chemical, biological, ergonomic and psychosocial. A biological hazard is a living organism or its product that can cause disease: bacteria in a cooling tower, blood in a first aid incident, mould in a damp building, contaminated soil on a construction site. Naming the category is not the point; noticing the hazard is.
Construction risk assessment: how this shows up on a site
Construction site hazards cluster round the same few things year after year: falls from height, being struck by a moving vehicle or load, collapse, contact with electricity, and exposure to dust including silica and asbestos. That is why the risk assessment and method statement a principal contractor asks for is mostly about those, and why a generic document that does not mention them is obviously not about your site.
Other questions people ask
What is the difference between a risk and a hazard?
A hazard is something with the potential to cause harm. A risk is the likelihood that it will, combined with how bad the harm would be. Hazards are identified; risks are evaluated.
What is an example of a biological hazard?
Legionella bacteria in a water system, bloodborne viruses in a needlestick injury, mould spores in a damp building, or leptospira in water where rats are present. Each is a living thing or its product that can cause disease.
Is a risk the same as a hazard in law?
No, and the regulations use them precisely. Regulation 3 of the Management of Health and Safety at Work Regulations 1999 requires an assessment of risks, which is why identifying hazards alone does not discharge the duty.
What is the difference between hazard and risk, in one example?
A hazard is something with the potential to cause harm; the risk is how likely that harm is and how bad it would be. A bottle of bleach on a shelf is a hazard and the risk is close to nothing; the same bottle decanted into an unlabelled jug in a kitchen is the same hazard at a much higher risk. That is why controls act on different halves of the sentence: a lock reduces the chance, a smaller container reduces the severity, and labelling reduces both. An assessment that lists hazards and stops has written the first half.
How do hazards and risks differ once you write them down?
The hazard is a thing, so it is written as a noun: the chemical, the height, the moving part. The risk is a judgement about that thing in your building, so it needs two numbers and a population: how likely harm is and how bad it would be, to whom. A list of hazards with no likelihood and no severity against them is an inventory rather than a risk assessment, and it is the commonest defect in the ones that get handed over.