Is it safe to work 12-hour shifts?

Safety of 12-Hour Work Shifts

Working 12-hour shifts carries significant safety risks, particularly for night shifts, with documented increases in fatigue, impaired performance equivalent to legal intoxication, cardiovascular disease risk, and compromised driving safety—these risks can be mitigated but not eliminated through strategic scheduling and fatigue countermeasures. 1, 2

Critical Safety Concerns

Performance Impairment

• Prolonged wakefulness of 18 hours produces cognitive impairment approximately equivalent to a blood alcohol concentration of 0.1%, which most workers reach or exceed during 12-hour shifts when accounting for commute and pre-shift activities 1, 2, 3
• Fatigue negatively affects reaction time, hand-eye coordination, clerical accuracy, memory, and reasoning—all critical for workplace safety 1, 2
• Studies comparing 8-hour versus 12-hour shifts among nurses demonstrated increased fatigue and specific safety concerns associated with the longer shifts 1, 2

Night Shift-Specific Hazards

• Night shift nurses working 12-hour shifts show significantly greater lane deviation during post-shift driving compared to day shift nurses, representing a key indicator of collision risk 4
• Workers on midnight-to-8AM shifts experience maximum impairment between 5-6AM when circadian drive for sleep is strongest 3
• Circadian rhythms require at least one week to accomplish an 8-hour phase change, meaning workers on consecutive overnight shifts cannot physiologically adapt 1, 2, 3

Long-Term Health Consequences

• Shift work increases cardiovascular disease risk by 40% compared to day workers based on a review of 17 studies 1
• Night shift work is classified as probably carcinogenic (Group 2A) by the International Agency for Research on Cancer, with associations to breast, prostate, colon, and rectal cancers 5
• Altered light-dark schedules are immunosuppressive, induce chronic inflammation, and alter cell proliferation and death 5

Risk Mitigation Strategies

Scheduling Approaches

• If the workforce is large enough, schedule single overnight shifts rather than consecutive ones to prevent cumulative sleep deprivation 1, 2
• Ensure strict adherence to shift time limits including sign-out times to prevent extension beyond 12 hours 2
• Maintain adequate respite between day and night shifts 2
• Consider that specific shift sequencing can minimize fatigue buildup—the design of the rotation matters as much as shift length 6, 7

Immediate Countermeasures

• Implement strategic napping in call rooms after overnight shifts before driving home 1, 2, 3
• Provide exposure to bright artificial light (at least 2500 lux) during night shifts, especially toward the end, to improve alertness 3
• Ensure adequate nutrition, hydration, and rest breaks during the workday 2

Organizational Support

• Maintain appropriate staffing ratios to prevent excessive workload 2
• Balance heavy workloads through flexible scheduling or rotation between high and low-stress environments 2
• Provide easily accessible mental health resources that are voluntary and free of stigma 2
• Monitor high-risk groups including less-experienced workers, those in direct patient contact roles, and staff without strong social support 2

Important Caveats

Worker Preference vs. Safety

• Many workers prefer 12-hour shifts despite documented evidence of increased fatigue and safety concerns, creating tension between employee satisfaction and objective safety data 2, 6
• Some studies show improvements in psychological health and reduced tiredness with well-designed 12-hour systems, but these benefits may come at the cost of acute safety risks 8

Context-Dependent Outcomes

• The safety of 12-hour shifts depends heavily on shift start times, pattern of shifts, amount of overtime, type of work, and workforce demographics—no single answer applies universally 7
• Circadian rhythm disruption is a biological reality that cannot be fully overridden by determination or professional commitment 2

Measurement Challenges

• Self-reported sleep logs overestimate sleep time by approximately 1.5 hours per night, making objective measurement through wrist actigraphy important for accurate assessment 5
• Total sleep time might increase with 12-hour shifts while domestic life deteriorates, or safety improves while health outcomes worsen—the outcome measured determines the conclusion 7