Emergency stops: testing them and what PUWER expects

It's Wednesday morning. A new starter on the wrapper sees a pallet tipping and hits the e-stop. The turntable slows, then keeps going for another half turn. Nobody's hurt. The pallet goes over and the shift carries on.

Later someone has a look. The mushroom head is cracked and the contact block behind it has been sticking for weeks. Nobody knew, because nobody had pressed it since the last time the wrapper was installed.

That's the trouble with an e-stop. It sits there for months doing nothing, and you only find out it's broken on the one day it matters.

What the law asks for

PUWER deals with stops in two regulations. Regulation 15 covers the normal stop. It must bring the machine "to a safe condition in a safe manner", and it must win over any start control (regulation 15).

Regulation 16 is the emergency stop. Where it's appropriate, the machine needs one or more readily accessible e-stops. The exception is where the hazards and the stopping time make one pointless. And the e-stop has to "operate in priority" over the normal stop (regulation 16).

The code of practice fills in the detail. Where your risk assessment says you need one, there should be an e-stop at every control point and at other places around the machine, so people can act fast (L22, paragraph 176). They should be easy to reach and easy to use (L22, paragraph 178).

What an e-stop is for, and what it isn't

Three lines in L22 settle most arguments on the shop floor.

An e-stop "should not be considered as a substitute for safeguarding" (L22, paragraph 175). If the only thing between a hand and the rollers is a red button, the guarding is wrong.

E-stops should not be used to stop the machine in normal running (L22, paragraph 177). You'll know the operator who stops the line on the e-stop at every break because it's nearer than the stop button. That wears the contacts and teaches everyone the button is routine.

And an e-stop is not isolation. HSE says interlocked guards and emergency stop controls are not suitable as a means of isolating a machine (L22, paragraph 195). If someone's going inside, the isolator goes off and gets a lock. Our guide to safe isolation covers the rest.

Reset must not mean restart

Pull the button back out. What happens?

It should be nothing. PUWER says a start, including a restart "after a stoppage for any reason", must need a deliberate action on the start control (regulation 14). So releasing the e-stop and resetting the safety relay should leave the machine ready to run but not running. Somebody then has to press start.

If your conveyor lurches into life the second the button is twisted out, that's a fault. Write it up and fix it before the next shift.

Faults in the circuit

Most e-stop circuits now run through a safety relay or a safety PLC, with two channels and monitoring. That's there for a reason. The control system has to be chosen with the faults you'd expect in mind. A fault or a loss of power must not add to the risk, and the control system must not get in the way of the stop or the e-stop (regulation 18). L22 puts it as "minimised failure to danger" (L22, paragraph 193).

Here's where breakdowns get dangerous. The safety relay won't reset, the line's been down an hour, and the fitter on shift has never traced a dual-channel circuit. Someone suggests a link wire across the contacts "just till the morning".

Don't. A bridged e-stop looks fine. It runs, it makes product, and nobody can tell until the day someone hits it and nothing happens. The cost of that link wire is far bigger than the cost of the downtime.

This is the night you need someone who reads safety circuits for a living. Our fault-finding guides on e-stop circuits that won't reset and safety relays and light curtains are a good start. If nobody on shift is confident, get help in rather than guess.

How to test them

PUWER doesn't give you a test interval for e-stops. It gives you the duty and expects you to set the interval from the risk.

The maintenance guidance is blunt. Safety features should be checked often, because a production fault shows itself quickly but "a fault in a safety-critical system could remain undetected unless appropriate safety checks are included in maintenance activities" (L22, paragraph 71).

Where a machine needs inspecting under regulation 6, the inspection should cover the safety-related parts (L22, paragraph 87). That can mean a functional test to check that "interlocks, protection devices, controls etc are working as intended" (L22, paragraph 89). The results of those inspections must be recorded and kept until the next one* (regulation 6).

In practice, a good e-stop test looks like this:

1. Run the machine in a normal state, with someone stood clear and ready on the isolator.
2. Press each e-stop in turn, wherever it is. The pull-cords and the remote stations at the far end count too.
3. Watch what stops and how fast. Does every hazardous motion stop? Does anything coast on longer than it did last time?
4. Check the HMI or the safety relay shows the right station.
5. Release and reset. Make sure the machine stays stopped until someone presses start.
6. Write down the date, the station, the result and who did it.

Stopping time is the one people skip. A motor brake that's wearing shows up as an extra half turn long before it fails. If you note the stopping time each test, you'll see the drift.

Here's what we think

Test every e-stop on a fixed cycle, set by the risk, and put it on the PPM sheet as its own task with its own line. A loose "check safety devices" line gets ticked without anyone pressing anything.

Make the test a two-person job. One presses, one watches the machine. Rotate who does it so more of the team know the safety circuits on each line. The more people who understand them, the fewer link wires you'll find in the panels.

And when one fails, treat it as a breakdown. Machine stops, defect gets fixed, then it goes back to work. A red button that doesn't work is worse than no button at all, because people trust it.

What to do on Monday

1. Pick your three busiest machines. Press every e-stop on each one with someone watching, and write down what happened.
2. Check each PPM sheet has an e-stop test as its own line, with a stopping time to record.
3. Ask your shift fitters which safety circuits they're not confident with. Get help lined up for those before the next night they fail.
4. Open the main panels on those machines and look for link wires across safety relay terminals.

* Inspection record rules correct as of 27 October 2026. Check PUWER on legislation.gov.uk for the latest. Paragraph numbers refer to L22, fourth edition (2014, amended 2018).