Dynamic risk assessment: what to do when work changes
A risk assessment written before work starts is based on the conditions expected at that point. The access route may be clear, the right people available and the planned equipment in place. On the day, a delivery blocks the route, rain changes the ground or another trade enters the work area. The useful question is not whether the original paperwork has been signed. It is whether its controls still work for the job that is actually happening.
Dynamic risk assessment is a common name for the ongoing judgment and action used when conditions change. It does not mean guessing quickly or accepting a new hazard because there is pressure to finish. It means noticing the change, checking the risk, choosing workable controls, communicating them and updating the plan when necessary.
The Health and Safety Executive's risk-assessment guidance says to review controls if they may no longer be effective or workplace changes could introduce new risks. It also advises considering workers' reports, accidents and near misses. “Dynamic risk assessment” is a practical description of that in-the-moment review; it is not a separate universal form named in every regulation.
What a dynamic risk assessment does
The purpose is to keep the work aligned with the controls that protect people. A worker or supervisor identifies a change from the planned situation, asks who could be harmed and how, then decides whether to continue with a changed control, pause and seek help, or stop the affected work until a safer method is agreed.
The process may take seconds for a minor change or require a wider team discussion and revised written method for a major one. It should be proportionate to the risk. An unplanned person walking into a segregated work zone calls for immediate action, not a lengthy scorecard. Replacing one approved material with a more hazardous substance may need a new COSHH review and instructions before the work resumes.
It also depends on competence and authority. A worker can notice a hazard and make the area safe without being authorised to redesign a lifting operation, energised electrical task or confined-space entry. The escalation route should be clear before those activities begin.
Dynamic assessment and the original written assessment
The initial risk-assessment process identifies foreseeable hazards, people at risk and planned controls. It should inform equipment, training, supervision and the method of work. Dynamic reassessment tests those controls against reality. They complement each other.
Do not use the word “dynamic” as an excuse to skip proper planning. Many foreseeable changes can be considered before the job starts. For outdoor work, weather and ground conditions may change. For occupied buildings, public access and overlapping contractors need thought. Good initial planning sets trigger points and options so staff know when to pause or escalate.
Nor should every fleeting observation lead to a new standalone document. HSE says employers with five or more people must record the significant findings of their risk assessment. It also says to update the record with changes made after review. The need to document a particular change depends on its significance and the work. A new substantial hazard, changed control or altered method should be captured in the relevant assessment and communicated to the people affected. A brief, controlled adjustment may be recorded in a task briefing or site log where useful. Follow any more specific permit, construction or sector requirements that apply to the job.
HSE's review guidance explains when changed controls or workplace conditions call for review. This page focuses on the decision at the point a change is noticed.
A five-question pause before continuing
1. What changed? Name the difference from the planned task. “The area feels unsafe” may be a useful warning, but try to identify the physical condition: a missing barrier, unexpected pedestrian route, defective tool, changed weather, new substance or additional contractor.
2. Who could be harmed, and how? Think beyond the person carrying out the task. Consider other workers, the public, occupants, delivery drivers and people who will use the area later. A control that protects your crew may move a risk into another work zone.
3. Do the planned controls still work? Compare the current condition with the assumptions in the written assessment or method. A barrier may no longer separate people from moving plant. A ladder may be unsuitable on the new ground. A safe isolation may be invalid after a system change. Do not rely on a control merely because it remains printed in the plan.
4. What can be changed safely now, and who must decide? Remove or reduce the hazard if possible. If a substantial change needs a competent person, supervisor or permit issuer, escalate. Do not improvise beyond training or authority. If the risk cannot be controlled with a suitable method, keep the affected work paused.
5. Who needs to know, and what record needs updating? Tell the people who will work under the changed method and those whose activities interface with it. Amend the relevant written assessment, method, briefing or permit when the changed risk and control are significant or a specific rule requires it. Make sure the current version reaches the workface.
This is a decision aid, not a universal statutory five-step formula. It helps turn a vague instruction to “do a dynamic assessment” into a clear conversation and action.
Example 1: a delivery changes the pedestrian route
A warehouse team has assessed loading-bay traffic and marked a pedestrian path. A delivery vehicle parks across it while workers are moving between buildings. The existing route and separation control no longer work. The person who notices should prevent people using the blocked route and inform the responsible supervisor. The team can then decide whether the delivery must move, a safe alternative route can be established, or the affected movement should pause.
This is more than a sign-off exercise. HSE's workplace transport guidance notes that a change in traffic routes or vehicles can create new risks and should prompt assessment. The site should consider the driver, pedestrians and other vehicles, communicate the temporary arrangement and decide whether the written traffic plan needs amendment. A quick instruction to “walk around it” could put pedestrians next to reversing vehicles and make the problem worse.
Example 2: wet ground changes a planned task
A team plans to use access equipment on firm, level ground. Heavy rain leaves part of the working area soft and uneven. The original assessment does not prove the equipment remains suitable on that surface. The team should pause the affected activity and assess the new condition against the manufacturer's instructions, the planned method and the competence of those setting up the equipment.
Possible outcomes include relocating to sound ground, changing the method or waiting for conditions to improve. Which option is suitable depends on the equipment, load, weather and site. This article cannot set a universal ground-bearing value or tell a team which access method to use. The important point is that the initial assessment's assumption has changed, so the control must be checked rather than carried forward on paper.
Example 3: another contractor enters the work area
A maintenance contractor has planned a task with an agreed exclusion area. Another company arrives early and starts work on a nearby service. The new overlap may affect isolation, access or emergency arrangements. Each contractor may have a sound document for its own job, yet the combined activities create a new interface risk.
The responsible people should coordinate before both tasks proceed. Clarify which services are affected, who controls the area, whether the sequence or isolation must change and how each crew will be informed. If a permit or task method relied on the area being empty, review it. A dynamic assessment should identify this mismatch promptly, while the formal plan records the lasting change if the jobs will continue together.
When the change requires a written update
There is no single rule that says every verbal dynamic assessment needs a new form. HSE focuses on effective control and on recording significant findings where five or more people are employed. Ask whether the change affects a material hazard, removes or changes an important control, changes the work method, or will continue for more than a brief interruption. If so, update the assessment or related controlled document and brief the people affected.
Specific work may have additional document rules. A permit to work may need reissue if the conditions that justified it no longer hold. Construction method statements, lifting plans and safe work method arrangements may need competent review. A COSHH assessment may need amendment when the substance or exposure changes. Do not assume a casual site note replaces those requirements.
Keep the record useful. State what changed, what risk it created, what control was agreed, who authorised it where needed and who was told. If the change exposed a wider weakness in the original plan, feed it back into the standard assessment so the next job starts from better information.
Who should make the decision?
Workers should be encouraged to report changed conditions and can take safe immediate action within their training. Supervisors coordinate work, verify that planned controls still fit and involve a competent person where the decision needs technical judgment. Employers need arrangements that make pausing and escalation possible rather than rewarding people for working around a hazard.
Define the boundaries in advance. The team should know which changes can be managed within the planned method, which require a supervisor, and which require the affected work to stop until a specialist or permit issuer has reviewed it. HSE's risk-management guidance asks businesses to put controls into practice and review them when circumstances change. That task is shared through the organisation; it is not solved by instructing the least experienced worker to “use common sense”.
Common mistakes
Treating the initial form as permanent permission. A dated form may describe yesterday's conditions. Look for changed assumptions and control failures.
Using a risk score instead of a decision. A number may help some teams prioritise, but it does not remove a hazard or tell workers what to do. Do not invent a legal requirement to calculate a 5 by 5 score.
Continuing while a major question is unanswered. If a changed condition makes the method uncertain, pause the affected work and escalate. Pressure to meet a deadline is not a control.
Changing a method without telling the crew. The best revised control fails if the next shift or subcontractor still follows the old plan. Communication is part of implementation.
Keeping every lesson local. Repeated on-the-spot fixes signal a predictable problem. Update the baseline assessment, equipment, access or planning so the same hazard does not surprise every crew.
Putting it into a repeatable work process
Before work, identify likely change triggers and decision owners. During work, make it normal to call out changed conditions, ask the five questions and pause the affected activity when controls no longer fit. Afterwards, record significant changes, brief others and improve the baseline plan. This creates a learning loop between the written assessment and the actual job.
If you use software to organise assessments, ask for a demonstration of how it keeps the relevant version accessible and the decision trail clear. HSE's risk-assessment guidance remains the starting point for the employer's actual duty. Software cannot decide on its own whether a particular site control is adequate or remove the need for a competent on-site judgment.
Next step: Review your existing risk assessment and identify the conditions that would make its controls fail. Agree who can authorise a change, how the team will be briefed and when the written record must be updated.