SiteIt's the fourth night of four. Your engineer started at 7pm, slept badly in the afternoon because the bins came, and has been on their feet since a conveyor jam at midnight. At 5am the robot cell stops with a safety fault.
They're good. They've fixed this fault before. But they read the wrong line of the alarm list, reset the wrong relay, and it takes an hour longer than it should. Nobody gets hurt this time.
The pattern set that up weeks ago. Every rota decides who's on when the line stops, and how awake they'll be.
The three patterns you'll see
Most maintenance teams on 24-hour sites run one of three patterns. Each has its own trade-offs.
4 on 4 off. Twelve-hour shifts. Four days, four off, four nights, four off, or a split of days and nights inside each block. Engineers like it because they get long breaks and fewer trips to work. You get a full cover pattern with four crews. The cost is long shifts and runs of nights.
Days with on-call. Engineers work days, Monday to Friday, and take turns carrying the phone overnight and at weekends. It looks cheap, because you're not paying for a night engineer to sit about. It works on sites where breakdowns at night are rare. On a site where the line runs all night, the phone goes all night, and your day engineer comes in tired the next morning.
Continental. Shorter blocks that rotate fast, often two or three shifts of each type before moving on. Nights are shared out, so nobody does many in a row. Some engineers hate the constant change. Others prefer it to four long nights.
There are dozens of versions of each. The question is what yours does to the person holding the spanners at 5am.
The legal floor
The Working Time Regulations set the minimum. GOV.UK sums up the main limits.
- a maximum of 48 hours* a week on average, normally over 17 weeks*, unless the worker opts out (GOV.UK, maximum weekly hours)
- 11 hours* rest between working days, and either 24 hours* off each week or 48 hours* each fortnight (GOV.UK, rest breaks)
- night workers must not average more than 8 hours* in 24, and regular overtime counts in that average (GOV.UK, night working)
Two of those catch maintenance teams out. Night workers whose work involves special hazards or heavy mental or physical strain can't work more than 8 hours* in any 24-hour period. That limit isn't an average. You need a risk assessment to decide whether that applies to any of your work (GOV.UK, night working). And you must offer night workers a free health assessment before they start nights, and regularly after (GOV.UK, health assessments).
Shift workers changing from one shift to another may not get the full daily or weekly rest. Where that happens they may be owed compensatory rest instead (GOV.UK, compensatory rest). More on the detail in our post on working time rules and maintenance overtime.
Legal is the start
HSE puts it bluntly. Complying with the Working Time Regulations "alone is insufficient to manage the risks of fatigue" (HSE, fatigue). The duty to manage fatigue sits with you, whatever the engineers say they'd prefer.
HSE's shift work guidance, HSG256, gives good practice that hits each pattern differently.
On 4 on 4 off, the nights are the problem. HSG256 advises you to "limit 12-hour night shifts to 2-3 consecutive nights". Four in a row goes past that. It also suggests a limit of 2-3 consecutive shifts, then 2-3 rest days, where shifts are long, on nights or start early. If your crews run four nights straight, that fourth night is where we'd expect your worst fault-finding. It's also where your night breakdowns take longer.
On continental, the direction matters. HSG256 says there is "limited evidence" the body clock adapts faster to forward rotation, mornings to afternoons to nights, and that it "may help reduce sleep loss and fatigue". It also recommends rotating shifts every 2-3 days. Fast-rotating continental patterns fit that well.
On days with on-call, the risk hides. HSG256 notes that people on standby or on-call "may experience disrupted and/or poor quality sleep", whether they're called out or not. And when they have to be at the workplace, that time counts as working time. So the engineer who was called in at 1am and is back for 7am may already be short of their 11 hours.
Handovers are where it slips
Whatever the pattern, the change of shift is a weak point. HSG256 says poor handover may increase the risk of errors and accidents, especially "during plant maintenance" and when safety systems have been over-ridden.
Twelve-hour patterns have fewer handovers. Continental has more. Either way, make it a routine: open jobs, isolations still on, any safety device bypassed, and what's been tried. Our post on shift handovers between maintenance engineers has a simple format.
So which one?
Here's our view. There's no right pattern, and HSE says the same. But we'd steer you this way.
If your breakdowns cluster on nights and the line runs 24 hours, staff the nights. Days with on-call will burn out your best people and slow your fixes. Count your night call-outs over three months. If someone's being called in more than a couple of times a week, you need a night engineer.
If you run 4 on 4 off, look hard at the run of nights. Splitting the block into two days and two nights keeps the pattern people like and cuts the long run of nights.
If your team is small, any pattern has holes. Holidays and sickness on a four-crew rota leave a shift with nobody. Plan how you'll fill those gaps before they come, not on the night. Our post on night shift maintenance cover covers the options.
What to do on Monday
- Count your night call-outs for the last three months, and who took them.
- Check how many consecutive 12-hour nights each crew works. If it's more than three, look at splitting the block.
- Check every night worker has been offered a health assessment.
- Mark the shifts in the next three months where holidays leave nobody on, and book cover now.
* Working hours limits, rest periods and averaging periods correct as of 20 September 2026. Check GOV.UK and HSE's shift work guidance for the latest.