The Definition of Microsleep

Definition of Microsleep

A microsleep is a brief, involuntary episode of sleep that lasts from a fraction of a second up to about 30 seconds. During a microsleep, the brain briefly stops processing information from the outside world, even if the person's eyes are open. People often do not realize it has happened, although they may notice a head nod, a missed exit or a gap in their memory.

Microsleeps are a sign of serious fatigue. They are caused by sleep loss, long periods awake, shift work, night work, untreated sleep disorders such as sleep apnea, and certain medications. They are most likely during the body's natural low points, typically between about 2 a.m. and 6 a.m. and in the mid-afternoon.

In safety-critical work, a microsleep of just a few seconds can be catastrophic. At highway speed, a vehicle travels the length of a football field in about four seconds. Microsleeps have been linked to road crashes, mining and heavy equipment incidents, rail accidents and errors in healthcare and process control.

Warning Signs of Microsleep

• Frequent yawning and heavy eyelids.
• Long or slow blinks and difficulty keeping eyes open.
• Head nodding or jerking back up.
• Drifting out of a lane, missing signs or exits.
• Not remembering the last few minutes of driving or work.
• Slower reactions and poor concentration.

Preventing Microsleeps at Work

Organizational controls

• Fatigue management: use a fatigue risk management system (FRMS) that covers rostering, hours of work and fatigue reporting.
• Roster design: limit shift length and consecutive night shifts, provide adequate rest between shifts and avoid quick returns. See shift work fatigue.
• Journey planning: limit driving after long shifts, plan rest stops and use journey management for long trips.
• Fitness for duty: include fatigue in fitness-for-duty checks and let workers report fatigue without penalty.
• Technology: some operations use driver monitoring cameras, alertness tracking or wearables to detect drowsiness and warn the worker or supervisor.

Individual strategies

• Aim for 7 to 9 hours of sleep and protect sleep time before shifts.
• Stop driving or operating equipment at the first signs of drowsiness.
• Take a short nap of 15 to 20 minutes when it is safe, and use caffeine strategically.
• Seek medical advice for snoring, daytime sleepiness or suspected sleep disorders.

Opening a window, turning up the radio or chewing gum do not reliably prevent microsleeps. Rest is the only real fix.

Example of Microsleep

A haul truck operator at an open-cut mine was on the fourth of four night shifts. Around 4 a.m., the truck's onboard fatigue monitoring system detected several long eye closures and sounded an in-cab alarm, while also alerting the dispatch supervisor.

The supervisor radioed the operator, who admitted he had been nodding off. He parked the truck in a safe bay and was relieved by a standby operator. The mine reviewed its rosters and found that several operators were working overtime on top of night blocks. It capped overtime on night shifts and added a fatigue check at the start of each night.

Frequently Asked Questions: Microsleep

Can you have a microsleep with your eyes open?

Yes. During a microsleep, your eyes may stay open while your brain stops processing what you see.

What causes microsleeps?

The main causes are sleep deprivation, long hours awake, night and shift work, and sleep disorders such as obstructive sleep apnea.

How can drivers prevent microsleeps?

Get enough sleep before driving, avoid driving during your usual sleep hours where possible, take regular breaks and stop to rest as soon as you notice signs of drowsiness.