Machine risk assessment

You cannot choose the right safeguarding until you understand the risk. A risk assessment is the structured process of identifying the hazards a machine presents, estimating how serious the risk from each one is, deciding whether that risk is acceptable and, if not, choosing measures to reduce it. HSE-103 introduced risk assessment in general. This lesson applies it to machinery using the method that machine safety standards share.

CSA Z432:23 requires a risk assessment as the basis for safeguarding, and points to ISO 12100 for the method. Ontario's pre-start health and safety reviews, BC's safeguarding requirements and many employers' own programs also expect a documented machine risk assessment.

The risk assessment process

• Determine the limits of the machine. Define its intended use and reasonably foreseeable misuse, who will use it and with what training, the space it occupies and its interfaces with other equipment, the life-cycle phases, the materials processed, the speeds and the environment.
• Identify hazards. Go through every life-cycle phase and every task, and list the hazards: mechanical, electrical, thermal, noise, vibration, radiation, materials, ergonomics and environment. For each hazard, identify the hazardous situation (a person exposed to the hazard) and the hazardous event that could cause harm.
• Estimate risk. For each hazardous situation, estimate the severity of possible harm and the probability of that harm occurring, considering how often and how long people are exposed, the probability of the hazardous event and the possibility of avoiding or limiting the harm.
• Evaluate risk. Decide whether the risk is acceptable or whether further reduction is needed, using the organization's criteria and the standards.
• Reduce risk. Apply the three-step method from Lesson 3, then go back and check that the new measures have not created new hazards and that the remaining risk is acceptable.
• Document. Record the scope, the team, the hazards, the estimates, the measures chosen and the residual risk, and keep the document up to date as the machine or its use changes.

Who should be on the team

A machine risk assessment is a team activity. Operators know how the machine is really used, including the shortcuts. Maintenance workers know what goes wrong and what tasks require access. Supervisors know the production pressures. Engineers know the design and control system. A health and safety professional knows the standards and the method. Including the people who face the hazard is not just good practice; it finds hazards that the others miss, and it builds commitment to the controls.

Identifying tasks and hazards

The most common weakness in machine risk assessments is a narrow task list. Teams list normal production and forget everything else. A good task list includes start-up, normal operation, changeovers and setup, adjustments while running, inspection, troubleshooting, jam clearing, cleaning and sanitation, lubrication, tool changes, preventive maintenance, repair, calibration, teaching (for robots), and shutdown. For each task ask who does it, how often, how long it takes, which hazard zones they enter, what energy is present and whether the safeguarding still works during that task.

Estimating risk

Standards do not prescribe a single risk estimation tool. Many organizations use a risk matrix that combines severity and probability. Machine safety standards often use parameters that break probability into parts: how often and how long a person is exposed, how likely the hazardous event is, and whether the person can avoid or limit the harm. Severity is usually judged on the worst credible outcome, not the most likely one, because amputation and death are always credible around powered machinery.

From risk to required performance level

When a risk reduction measure depends on the machine's control system, for example an interlock that stops the machine when a guard opens, the control system must be reliable enough for the risk. ISO 13849-1 expresses this reliability as a performance level, from PL a (lowest) to PL e (highest). The risk graph in the standard turns the three parameters into a required performance level, written PLr, for each safety function. Lesson 7 explains what performance levels mean for the design of the control system.

Risk estimation pitfalls

Risk assessment is only as good as the honesty of the people doing it. Common pitfalls include rating severity on the most likely outcome rather than the worst credible one; assuming people will always follow procedures; ignoring tasks that are not in the manual, such as clearing jams; assuming a guard is effective without checking the safety distance; and rating avoidance as possible because experienced operators have never been hurt. A useful discipline is to ask what would happen if the most inexperienced worker did the task on the busiest day of the year.

Another pitfall is treating the risk assessment as paperwork for compliance. A risk assessment that sits in a binder does nothing. The result should drive real decisions: which guards to install, how interlocks are designed, what the lockout procedure says, what training covers, and what inspections check.

Documenting and maintaining the assessment

A machine risk assessment should record the machine and its limits, the team and date, the tasks and hazards, the risk estimates before and after measures, the measures selected with the required performance levels, the verification and validation carried out, and the residual risks and how they are communicated. It should be reviewed whenever the machine is modified, moved, used for a new product or process, after an incident or near miss, when standards change, and at a regular interval set by the organization.

The assessment also links to other documents: the lockout procedure for each machine, the safeguarding inspection checklist, operator training records, and, in Ontario, any pre-start health and safety review report. Keeping these documents consistent is part of a mature machine safety program.

Some organizations add a simple check to every risk assessment: for each hazard rated high, the team must name the specific engineering control that addresses it, the person responsible and the date. Hazards that can only be controlled by procedures or PPE are flagged for a second look by an engineer. This keeps the assessment focused on real risk reduction rather than paperwork.