Risk Assessment and Hazard Control
Hazards and risks, the risk matrix, the hierarchy of controls, a job safety analysis and a worked assessment of a grinding job.
Hazard, risk and harm
A hazard is anything that can cause harm: a spinning blade, a hot iron, a solvent, a live wire, a heavy load. Harm is the injury or illness. Risk combines how likely the harm is with how bad it would be. A spinning blade is always a hazard; the risk depends on whether it is guarded, whether your hands go near it, and how often. Safety work is the habit of finding hazards, estimating the risk, and reducing it before someone is hurt.
| Kind of hazard | Examples in a workshop | Typical harm |
|---|---|---|
| Mechanical | Blades, belts, pinch points, flying chips, falling parts | Cuts, amputation, crush, eye injury |
| Electrical | Mains wiring, damaged cords, capacitors, batteries | Shock, burns, fire |
| Thermal | Hot metal, soldering irons, welding, heat guns | Burns, fire |
| Chemical | Solvents, adhesives, acids, fumes, dust | Poisoning, burns, lung disease |
| Noise and vibration | Saws, grinders, compressors, impact tools | Hearing loss, hand-arm vibration syndrome |
| Radiation | Lasers, welding arcs, UV curing | Eye and skin damage |
| Ergonomic | Lifting, awkward postures, repetition | Back and joint injury |
| Human | Fatigue, rushing, distraction, impairment | Mistakes that cause all of the above |
Scoring risk: the matrix
A simple method scores the likelihood (1 rare to 5 almost certain) and the severity (1 negligible to 5 catastrophic), and multiplies them. The score gives a band: 1 to 4 low, 5 to 9 medium, 10 to 16 high, 17 to 25 extreme. It is rough, but it forces you to compare hazards and to see the effect of a control.
Worked example: an angle grinder
- Before: grinding with the guard removed. Likelihood of an injury is likely (4), severity of a broken disc or a cut is major (4): 4 × 4 = 16 (high).
- Controls: fit the guard, wear a face shield over safety glasses, clamp the work, use discs rated for the tool’s speed, and get training. Better still, replace grinding by a bandsaw or hacksaw cut where possible.
- After: the likelihood falls to unlikely (2) and the severity stays major (4): 2 × 4 = 8 (medium). The severity cannot go down because a disc can still break.
- The disc rating matters: a 125 mm disc rated for 80 m/s has a maximum speed of 4 800 ÷ (π × 0.13) = 12 223 rpm. A grinder running at 11 000 rpm drives the rim at 72 m/s, within the rating; a disc rated at 63 m/s would be 14 % over speed, and the stress in the disc goes as speed squared (1.31 times).
The hierarchy of controls
| Level | Approach | Example |
|---|---|---|
| 1. Eliminate | Remove the hazard | Buy pre-cut stock; do not do the task |
| 2. Substitute | Use something less dangerous | Water-based adhesive for solvent; a lower-voltage tool; a hacksaw for an angle grinder |
| 3. Engineering controls | Isolate people from the hazard | Guards, extraction at the tool, an enclosed laser, interlocks, an RCD |
| 4. Administrative controls | Change how people work | Training, procedures, signs, time limits, never working alone on risky jobs |
| 5. PPE | Protect the person | Glasses, ear defenders, respirator, gloves where appropriate (see Personal Protective Equipment) |
Work from the top. It is tempting to jump to a pair of gloves; the better question is whether the task can be done another way, or the hazard separated from the person.
A job safety analysis
A job safety analysis (JSA) breaks a task into steps and asks, for each, what could go wrong and how to prevent it. It takes ten minutes and is worth doing for any job you have not done before or any job with a significant hazard.
| Step | Hazard | Control |
|---|---|---|
| 1. Plan the cut and mark the stock | Sharp tools; poor lighting | Cap the knife; good light (see Shop Tools) |
| 2. Clamp the work | Trapped fingers; part not secure | Clamp to the bench; hands clear of the jaws |
| 3. Put on PPE | Eyes, ears, lungs | Glasses, ear defenders, mask |
| 4. Make the cut | Kickback; flying debris; noise; dust | Guard on; correct blade; extraction on; stand to the side |
| 5. Clear offcuts | Cut from the blade still turning | Wait for the machine to stop; use a push stick or brush |
| 6. Clean up | Dust; slips; fire from sawdust | Sweep or vacuum; empty the collector; no sweeping with compressed air |
Worked example: hazards per step
The six steps above have 12 to 18 hazards between them (about 2.5 per step: 15 in all). Each one has a control that was cheap to add: a clamp, a push stick, a switch on a strip. The JSA took ten minutes; listing them is what makes you see the ones you would have missed.
Ranking the hazards in a shop
Score every task, rank them and deal with the high ones first. The table is a worked set for a small shop: likelihood and severity before controls, the main control, and the score after it.
| Task | Before (L × S) | Main control | After (L × S) |
|---|---|---|---|
| Angle grinder, guard removed | 4 × 4 = 16 (high) | Fit the guard; face shield; clamp the work | 2 × 4 = 8 (medium) |
| Table saw ripping freehand | 3 × 5 = 15 (high) | Fence, riving knife, push stick; or use a bandsaw | 1 × 5 = 5 (medium) |
| Soldering in a closed room | 4 × 2 = 8 (medium) | Fume extractor; open window; wash hands | 2 × 2 = 4 (low) |
| Drilling a small part held by hand | 4 × 3 = 12 (high) | Clamp or vise; drill press | 1 × 3 = 3 (low) |
| Spray painting without ventilation | 4 × 3 = 12 (high) | Extraction hood; respirator; substitute water-based | 2 × 3 = 6 (medium) |
| Extension cord across the floor | 3 × 3 = 9 (medium) | Reroute; short cord; GFCI/RCD | 1 × 3 = 3 (low) |
| Oily rags in a bin | 2 × 5 = 10 (high) | Metal can with a lid; wash or dry flat | 1 × 5 = 5 (medium) |
Worked example: where to start
- Sorted by score the first are the grinder (16), the table saw (15), hand drilling and spray painting (12 each) and the oily rags (10): all four are in the high band.
- The oily rags score only 10 because a fire is unlikely, but it would be catastrophic and takes the whole shop. A metal can with a lid costs a few dollars. Rare but catastrophic hazards are worth controlling even when they feel unlikely.
- After the controls every task is at or below 8 (medium or low): the plan costs a few hundred dollars of guards, clamps and a metal can, and most of it is a change of habit.
Small chances add up
A one-in-a-thousand chance of injury on each use sounds safe. It is not, because the chance accumulates over every use: the probability of at least one injury in n uses is 1 − (1 − p)n.
Worked example: the cumulative chance
- With p = 1 in 1 000 per use, 200 uses a year for 20 years (4 000 uses) gives 1 − 0.9994 000 = 98 %: you will almost certainly be hurt once.
- A control that cuts the chance by a factor of ten (p = 1 in 10 000) brings the lifetime chance down to 33 %; by a factor of a hundred (1 in 100 000) to 3.9 %.
- Even over one afternoon of 50 uses, the chance is 4.9 %: small, but it is the same chance every time.
- Judge a habit by its lifetime risk, not by its next use.
Layers of protection
No single control is perfect. Several independent layers multiply: if each layer lets a fraction f of events through, two layers let through f1 × f2.
Worked example: guard and training
- A guard that stops 90 % of the contacts lets 10 % through (f1 = 0.1). A habit of keeping hands clear that works 90 % of the time also has f2 = 0.1. Together: 0.10 × 0.10 = 0.01, or one contact in a hundred.
- The layers must really be independent. If a common cause (tiredness, hurry) defeats both, with a probability of 0.05, the combined figure becomes 0.05 + 0.95 × 0.01 = 0.06: five times worse than the ideal. That is why rushing and fatigue are hazards in their own right (see First Aid, Emergencies and Safe Habits).
Review, records and training
- Write the assessment down: a one-page table like the one above, kept in the shop.
- Review after any incident, near miss or change (a new machine, a new material, a new person), and once a year.
- Near misses are free lessons. Record them and fix the cause before it hurts someone.
- Train anyone who uses a machine, and supervise them until they are competent; show them the stop and the guard before the start.
- Know the law. Employers have duties; a hobbyist has none until they have visitors, apprentices or customers, but the injuries are the same.
Worked example: time against injury
Five minutes of extra setup (clamping, fitting the guard) on 100 tasks a year costs 8 hours. A hand injury that keeps you out of the shop for 14 days and costs $1 500 in treatment and lost work is worth many years of that time. The control always costs less than the injury.
Troubleshooting
| Problem | Likely cause | Try |
|---|---|---|
| “I have always done it this way” | Normalization of risk: no injury yet | Do a JSA; look at the lifetime chance; ask what would happen if it went wrong |
| Guards are taken off | They get in the way or slow the job | Redesign the guard; give a better way to do the task (a jig, a push stick) |
| PPE not worn | Uncomfortable, not at hand, not enforced | Make it comfortable and stored where the task is; lead by example |
| Near misses not reported | Fear of blame | Treat them as lessons, not faults |
| The assessment is out of date | New tools or people | Review after each change and once a year |
| Too many hazards to fix | No priority | Score and rank; do the extreme and high ones first |
Related
- Workshop Safety: the overview of this guide.
- Personal Protective Equipment: the last line of defense.
- Machine and Hand Tool Safety: guards and safety distances.
- Machine Safety Systems (in the System Integration guide): risk graphs and performance levels for industrial machines.
FAQ
How do I do a risk assessment for my workshop?
List the hazards of each task, score likelihood and severity from 1 to 5, multiply, add controls from the top of the hierarchy and score again; write it down and review it yearly.
What is the best kind of control?
The one that removes the hazard or replaces it: eliminate and substitute come before guards, procedures and protective equipment.
Is PPE enough on its own?
No: it leaves the hazard in place and depends on being worn and fitting well. Use it as the last layer, not the first.
Why do I need a risk assessment for a hobby shop?
You do not need one by law, but the method finds the hazards you would otherwise miss; ten minutes can prevent an injury that lasts a lifetime.
References
- ISO 12100, Safety of machinery: general principles for design, risk assessment and risk reduction; ISO 45001 (occupational health and safety management).
- HSE (UK), Five steps to risk assessment; OSHA, Job Hazard Analysis (OSHA 3071).
- NIOSH, Hierarchy of Controls.
Last reviewed: October 2026. The scores and probabilities are examples: judge your own tasks.