Fatigue Is Impairment: What 24 Hours Awake Does to a Worker (2026)

Being awake for 17 hours impairs performance to roughly the same degree as a blood alcohol concentration of 0.05 percent. At 24 hours awake it is equivalent to about 0.10 percent, which is above the legal driving limit in Canada.

No crew would let someone work drunk. The same crew will routinely let a worker finish hour nineteen of a storm shift, and the measured impairment is comparable. Fatigue is not tiredness with a bad attitude attached, it is a form of impairment.

What the research actually established

The equivalence comes from work published in Nature in 1997, which found that extended periods of wakefulness between 17 and 24 hours impair performance to an extent equivalent to alcohol ingestion.

The detail worth knowing is the rate. Each additional hour awake between 10 and 26 hours produced a performance decrement equivalent to a 0.004 percent rise in blood alcohol concentration. The impairment accumulates steadily rather than arriving at a threshold, which is why nobody notices crossing it.

Two practical markers come out of the wider literature. Workers who slept less than five hours before work, or who have been awake more than 16 hours, have a significantly higher chance of making mistakes. And the Government of Alberta notes that most incidents occur between midnight and 6 a.m., when people are most likely to feel tired.

Fatigue impairs memory, attention span, coordination, reaction time and information processing. It also increases irritability and reduces motivation, which means a fatigued worker is not simply slower, they are more likely to cut corners and skip procedures.

Hours of service measure the wrong thing

This is the gap that catches compliant employers, and it applies well beyond trucking.

Hours-of-service style rules regulate time on duty. They do not regulate time awake. A worker can be entirely within their permitted hours and still be badly impaired, because the clock started when the shift did and they had already been up for eight hours.

Most Canadian industries have no hours-of-work limit at all for safety purposes. Outside federally regulated transport, there is generally no ceiling on how long a crew can run, which leaves the decision to a supervisor at 2 a.m. rather than to a rule.

That is why fatigue belongs in the hazard assessment rather than in the staffing spreadsheet. Canadian industry guidance on managing fatigue treats it as a workplace hazard requiring controls, not as a personal problem workers bring to work with them.

The practical version: ask when the worker woke up, not when the shift started. Those are different numbers and only one of them predicts impairment.

The commute is the most dangerous part of the shift

Research on extended working hours and injury found that almost all nurses working 12-hour night shifts reported having at least one motor vehicle accident or near accident in the previous 12 months while driving to or from work.

That is the part fatigue management programs most often miss. The shift ends, the responsibility is treated as discharged, and the worker then performs the single highest-risk task of their day, alone, at the point of maximum impairment.

It is also the exposure most employers have the least appetite to address, because it happens off the clock. The controls that exist are unglamorous: a place to sleep before driving, a ride, a taxi, or a policy that says leaving late is better than leaving impaired.

Crews doing storm response, overnight maintenance and shift changeovers are the obvious cases. So is anyone driving home after a twelve-hour shift that started before dawn.

The things that make fatigue worse

Fatigue rarely acts alone, and several ordinary job-site conditions multiply it.

Cold is the clearest. A cold worker burns energy maintaining core temperature, and one of hypothermia's warning signs is confusion, which is indistinguishable from tiredness at hour fourteen. Our guide to cold stress at work in Canada covers the overlap, including why bulky clothing changes what a worker can safely lift.

Poorly fitting or worn-out equipment adds a load all day. A boot with a compressed midsole on concrete produces real fatigue by mid-afternoon, covered in our guides to what makes a comfortable work boot and insoles for long work shifts.

Noise, vibration and heat all add to the load, and respiratory protection increases breathing effort, which matters over a long shift. Our guide to respirator fit testing under CSA Z94.4 covers selection.

And night work compounds everything, because a worker is fighting both accumulated hours and a circadian low point. That is the combination behind the midnight-to-six pattern.

Where fatigue meets the serious hazards

Fatigue does not cause its own category of incident. It makes every other hazard more likely to land.

Work at height is the sharpest example. Reduced coordination and slower reaction on a ladder or a beam produces the fall, and then the rescue plan has to work, covered in our guide to suspension trauma and fall rescue.

Roadside and traffic control work combines fatigue, darkness and moving vehicles. Conspicuity matters more when a driver is also tired, covered in our guides to traffic control person equipment and CSA Z96 classes and levels.

Chemical handling suffers a subtler failure. A fatigued worker is more likely to reach for the nearest glove rather than the right one, which is precisely the decision our guide to choosing chemical resistant gloves exists to prevent.

Slips and trips rise too, because fatigue changes gait and attention to footing. Our guide to slip resistance at work covers the equipment half of that.

Controls that actually work

Schedule the highest-risk tasks away from the end of the shift and away from the midnight to six window. That single change costs nothing and moves the most demanding work to the hours when people can do it.

Build shift limits into the contract rather than deciding them during the event. A storm at 2 a.m. is the worst possible moment to judge how much longer a crew can safely run, because the person judging is impaired too.

Rotate demanding tasks across a crew rather than leaving them with whoever is fastest, and make rest breaks in a warm, quiet space an expectation rather than a concession.

Train people to recognize the signs: weariness, sleepiness, irritability, physical tiredness, and reduced alertness, concentration and memory. Irritability is the one most often read as attitude rather than as a symptom.

Then make it safe to say so. A worker who reports being too tired to continue and gets treated as unreliable will not report it again, and neither will anyone who watched. That is a supervision problem rather than a scheduling one.

What workers can control

Most adults need seven to nine hours of sleep, and the research marker is blunt: under five hours before a shift significantly raises error rates.

Night shift workers should get to bed as soon as practical after work rather than staying up, since delaying sleep after a night shift shortens it considerably. Keep a consistent sleep and wake schedule where the roster allows, limit screens before sleeping, and treat the sleep environment as equipment: dark, quiet, cool.

Caffeine works and it has a tail. Late-shift caffeine bought at hour ten is borrowed against the sleep that has to happen at hour fourteen.

Where fatigue is persistent despite adequate sleep, that is worth raising with a healthcare professional rather than managing indefinitely, since ongoing fatigue can have a medical cause.

For the wider picture on what should be in place before a shift starts, see the complete PPE checklist for Canadian workers, our guide to PPE requirements for Canadian construction sites, our guide to who pays for PPE in Canada and our guide to CSA Z1220 first aid kit requirements.

Frequently Asked Questions

Is fatigue really comparable to being drunk?

In terms of measured performance, yes. Research found 17 hours of wakefulness impairs performance equivalently to a blood alcohol concentration of about 0.05 percent, and 24 hours to about 0.10 percent, which is above Canada's legal driving limit of 0.08 percent. CCOHS treats fatigue as a form of impairment.

How much sleep loss starts to matter?

Studies indicate workers who slept less than five hours before a shift, or who have been awake more than 16 hours, have a significantly higher chance of making mistakes. Impairment accumulates gradually rather than at a threshold, at roughly the equivalent of a 0.004 percent rise in blood alcohol for each additional hour awake.

Do hours-of-service rules prevent fatigue?

Not on their own. Those rules regulate time on duty, not time awake, so a worker can be fully compliant while badly impaired because they had already been up for hours before the shift began. Most Canadian industries have no general hours-of-work limit for safety purposes at all.

When do most fatigue-related incidents happen?

The Government of Alberta notes that most incidents occur between midnight and 6 a.m., when people are most likely to feel tired. High-risk and demanding tasks should be scheduled away from that window and away from the end of a long shift where the work allows.

What about the drive home?

It is often the highest-risk part of the shift. Research on nurses working 12-hour night shifts found almost all reported at least one motor vehicle accident or near accident in the previous year driving to or from work. Controls include somewhere to sleep before driving, a ride, or a policy that leaving late beats leaving impaired.

What are the signs to watch for?

Weariness, sleepiness, irritability, physical tiredness, and reduced alertness, concentration and memory. Irritability is the one most often mistaken for attitude. Fatigue also reduces motivation, which makes cutting corners and skipping procedures more likely.

This guide is general workplace safety information, not medical or legal advice. Persistent fatigue despite adequate sleep should be discussed with a healthcare professional. Hours of work and fatigue management obligations are set by federal, provincial and territorial legislation and vary by industry; confirm yours with the authority that governs your workplace.