SiteIt's 4.15am. There's a bang from the baler, then a hiss. By the time anyone gets there, a hose on the main ram has split. There's a fine mist of oil in the air, a slick spreading across the floor, and the pump is still running.
Someone's already walking towards it with a rag.
That's the moment this goes one of two ways. A hydraulic failure is one of the few breakdowns where the first thing people do on instinct can put them in hospital. The repair can wait ten minutes. Use them to stop anyone getting hurt.
Minute one: stop the pump, stop the people
Hit the stop and kill the pump. Then keep everyone back, including the person with the rag.
The danger is the oil you can't see. A jet from a pinhole or a split hose can go through skin. HSE warns that "even pinprick punctures in pipework can cause major injury", and lists "searching for leaks with bare hands" as a common mistake (HSE, fluid injection). Never run a hand along a hose to find a leak. Use a piece of card or wood, with the system depressurised.
HSE's safety alert on injection injury says serious cases have been reported at pressures over 100 bar*. It adds that anecdotal evidence suggests injury may happen at pressures as low as 7 bar* (HSE safety alert).
If someone's been hit
Treat any injection as an emergency, even if it looks like a pinprick. The same alert says prompt action is needed to save the injured person's limb, or even their life. Without treatment, after four to six hours* the pain can get intense, and injection injuries can lead to amputation (HSE safety alert).
So get them to hospital straight away, and tell A&E it's a high-pressure injection injury. Send the oil type with them if you can. Don't let anyone wait to see if it gets worse. Everyone who works on hydraulics should know this before the night it happens, and the alert says so too.
Minutes two to five: what's still holding energy?
Stopping the pump doesn't make the machine safe. Hydraulics can hold energy long after the motor stops.
Check for:
- an accumulator that's still charged
- a ram, platen, table or boom that's raised and held up by oil
- trapped pressure between a closed valve and a cylinder
- a load that will drop if a hose is opened
HSE's code of practice for PUWER says where work equipment relies on hydraulic or pneumatic pressure, you should provide a means of isolation. Where possible, there should be a way to dissipate stored energy too (L22, paragraph 199). It gives the example of machines that hold hydraulic energy which, under fault conditions, can cause movements nobody intended (L22, paragraph 173). So find the dump valve, and know where the accumulator bleed is. Prop or pin anything that's raised before anyone goes near it. HSE's design advice calls for check valves and mechanical supports that are easy to use from outside the danger area (HSE, fluid injection).
Then isolate and lock off as you would for any job. If you need a refresher, our post on safe isolation covers it. Prove the pressure is gone on a gauge before you crack a fitting. Crack it slowly, wrapped in a rag, with your face out of line.
Minutes five to ten: the floor and the drains
Now deal with the oil. It's a slip hazard for everyone, including the engineer who comes to fix it. Put out absorbent, cone the area, and stop forklifts running through it.
Look for drains. Oil going down a surface water drain turns a breakdown into a pollution problem, so block or cover any drains nearby. If the mist reached anything hot, check for smoke and keep an extinguisher handy.
Then take photos. The split hose, the fitting, where the oil went, the pressure on the gauge if it's still showing. These help work out why it failed.
Don't put the old fitting back
Here's where the next injury comes from. The fitting that blew off looks fine. Someone wants to screw it back on and run.
HSE's safety alert on a fatal injection injury is blunt about it. When replacing or maintaining a pressurised system, fittings should be "matched and compatible as per the original equipment manufacturers specification". It also says checking the replacement should be treated as a pressure test, with the right precautions (HSE safety alert). HSE's other guidance lists using the wrong couplings, makeshift repairs and failing to replace damaged hoses as common errors (HSE, fluid injection).
So the hose gets replaced with one of the right rating, length and fittings. If you don't have it on the shelf, you either get one made up or wait. A jubilee clip and tape is not a repair. Our post on the part that isn't on the shelf covers your options at that hour, and critical spares covers what to hold next time.
One more point. Hydraulic oil doesn't fall under the pressure systems rules. HSE says relevant fluids under those regulations "do not include hydraulic oils" (HSE, PSSR). So there's no written scheme of examination catching your worn hoses. Your own inspections and maintenance under PUWER are what catch them.
Who fixes it
A hose swap is a fitter's job if they have the hose and know the system. A pump that's failed, a valve that's sticking or a cylinder that drifts is a different job. That needs someone who understands hydraulic circuits, can read the schematic, and knows how to set relief pressures safely once it's back together.
If that isn't on your shift tonight, call for help early. A hydraulic machine down for six hours while someone works it out costs far more than a callout. And a fitter guessing at relief valve settings is a risk to everyone stood near it when it restarts.
After the restart, look at why it failed. A hose rubbing on a bracket, oil running hot, or a hose past its life. Our posts on hydraulic leaks and hydraulic oil running hot are good places to start.
What to do on Monday
- Brief every shift on injection injuries: no hands on hoses, and straight to A&E if anyone's hit.
- Mark the dump valve and accumulator bleed on every hydraulic machine, and make sure the props are next to it.
- Put a spill kit near each hydraulic machine, and check where the nearest drains are.
- Check you hold made-up hoses, or a supplier who'll make them at night, for your worst machines.
* Injection injury pressures and the four to six hour figure correct as of 15 October 2026. Check HSE's safety alert on hydraulic injection injury for the latest. Paragraph numbers refer to L22, fourth edition (2014, amended 2018).