A dynamic risk assessment is the judgement a worker makes on the spot, while the job is running, when what they find does not match what was planned. It matters in work where conditions change faster than paperwork can: emergency response, lone visits to unfamiliar premises, maintenance in occupied buildings, and any job where the first five minutes on site reveal something the office did not know.
Why the written assessment is not enough on its own
A written risk assessment is made before the work, from what was known then. It cannot anticipate the locked gate, the tenant who did not move the furniture, the standing water in the basement, or the second contractor who turned up on the same day. Dynamic assessment is the recognised answer to that gap, and it is a skill rather than a document.
What doing it properly looks like
Stop before entering. Read the situation against what was expected. Decide whether the planned controls still work. If they do not, either adapt within your competence and authority, or stop and escalate. The last option is the one that has to be genuinely available: a worker who knows that stopping will be treated as a failure will not stop, and the assessment becomes theatre.
How it is recorded
Usually it is not recorded in the moment, which is the point. What gets recorded is the outcome: the job was done as planned, or it was changed and here is how, or it was stopped and here is why. Firms that make this work capture those changes and feed them back into the written assessment, so the next version of the document knows what the last visit found.
Questions people ask about dynamic risk assessment
Is a dynamic risk assessment a legal requirement?
The regulations do not use the phrase. They require a suitable and sufficient assessment and require it to be reviewed when it is no longer valid, and dynamic assessment is how that duty is met in work whose conditions change on site.
Does a dynamic risk assessment replace the written one?
No. It sits on top of it. A business relying on dynamic assessment alone has no baseline to judge the changes against, and no record of what the significant findings were.
Who can carry out a dynamic risk assessment?
The person doing the work, provided they have been trained to recognise the hazards involved and have real authority to stop. Both halves are needed; either one alone does not work.