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Fatigue Risk Calculator: Folkard-Lombardi Scoring with Regulatory Frameworks

Assess Shift Fatigue Risk Using API RP 755, NRC, FMCSA, and EU WTD Standards with BAC Equivalence Display

Free fatigue risk calculator for safety managers, operations supervisors, and HSE professionals in industries where worker fatigue is a safety-critical risk factor. Uses the Folkard-Lombardi fatigue scoring model to quantify cumulative fatigue based on shift length, time of day, rest between shifts, and consecutive work days. Checks your schedule against four major regulatory frameworks: API RP 755 (petroleum/chemical), NRC 10 CFR 26 (nuclear), FMCSA HOS (commercial motor vehicles), and EU Working Time Directive.

Fatigue impairment is invisible until something goes wrong. Research shows that 17 hours awake produces cognitive impairment equivalent to a 0.05% blood alcohol concentration, and 24 hours awake equals 0.10% BAC — legally drunk in every state. This calculator displays the BAC equivalence for your shift pattern so you can communicate fatigue risk in terms everyone understands. A plant manager might shrug at a "fatigue score of 7.2" but will pay attention when you tell them their night-shift operators are performing at the equivalent of 0.08% BAC by the end of their rotation.

Pro Tip: The most dangerous shift in any rotation is the first night shift after flipping from days. Circadian disruption peaks during this transition because the body's internal clock still expects sleep. If your schedule has a quick turnaround from day shift ending at 3 PM to night shift starting at 11 PM (only 8 hours off), the Folkard-Lombardi score for that first night shift is 30-40% higher than subsequent night shifts. Push for at least 24 hours off before a day-to-night transition.

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Shift Fatigue Risk Estimator
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How It Works

  1. Enter Shift Pattern

    Input the start time, end time, and duration for each shift in the rotation. Include day shifts, night shifts, and any overtime extensions. The model evaluates each shift individually and cumulatively.

  2. Specify Rest Periods

    Enter the hours of rest between consecutive shifts. Short rest periods (under 11 hours) significantly increase fatigue scores. The calculator flags rest periods that violate regulatory minimums.

  3. Set Consecutive Work Days

    Enter the number of consecutive days worked before a rest break. Extended runs of 7+ consecutive days compound fatigue even when individual shifts are within normal length.

  4. Select Regulatory Framework

    Choose the applicable standard: API RP 755 for refineries and chemical plants, NRC for nuclear facilities, FMCSA for commercial drivers, or EU WTD for European operations. The calculator checks your schedule against that framework's specific limits.

  5. Review Fatigue Score and BAC Equivalence

    See the Folkard-Lombardi fatigue index for each shift and the cumulative score across the rotation. The BAC equivalence translates the fatigue level into impairment terms that are immediately understandable.

  6. Identify Violations and Recommendations

    The calculator flags any shifts or rest periods that violate the selected regulatory framework and suggests modifications to reduce fatigue risk.

Built For

  • Refinery safety managers evaluating whether a proposed shift schedule complies with API RP 755 fatigue management requirements
  • Nuclear plant schedulers verifying that operator work hours stay within NRC 10 CFR 26 limits during outage overtime
  • Fleet safety directors checking that driver schedules comply with FMCSA hours-of-service rules and rest requirements
  • HSE professionals presenting fatigue risk data to operations managers using BAC equivalence to communicate the severity
  • Plant managers comparing the fatigue risk of 8-hour vs 12-hour rotation schedules before making a permanent change
  • Incident investigators evaluating whether worker fatigue was a contributing factor in a workplace accident
  • Union safety committees reviewing proposed schedule changes for fatigue risk before agreeing to new rotation patterns

Features & Capabilities

Folkard-Lombardi Fatigue Model

Quantifies fatigue based on shift duration, time of day (circadian factors), cumulative hours, and rest between shifts. Produces a numerical fatigue index score for each shift and the overall rotation.

4 Regulatory Frameworks

Checks schedules against API RP 755, NRC 10 CFR 26, FMCSA HOS, and EU Working Time Directive. Flags violations and shows which specific rule is exceeded.

BAC Equivalence Display

Translates fatigue scores into blood alcohol concentration equivalence based on published research. Makes fatigue risk immediately understandable to non-technical audiences.

Shift-by-Shift Breakdown

Shows the fatigue score for each individual shift in the rotation so you can identify the highest-risk shifts and target schedule modifications.

Rest Period Analysis

Evaluates rest time between shifts against regulatory minimums and fatigue recovery thresholds. Short rest periods are the most common cause of cumulative fatigue buildup.

Frequently Asked Questions

The Folkard-Lombardi model is a biomathematical fatigue scoring system that accounts for shift duration, time of day (circadian rhythm effects), cumulative work hours, and rest between shifts. It produces a numerical index where higher scores indicate greater fatigue-related impairment risk. The model is widely used in the petroleum, nuclear, and transportation industries for shift schedule design and regulatory compliance.
Research by Dawson and Reid (1997) established that 17 hours of sustained wakefulness produces performance impairment equivalent to a BAC of 0.05%. At 24 hours awake, impairment equals 0.10% BAC, which exceeds the legal driving limit in all US states. Night shift workers who have been awake since the previous morning are effectively working impaired, which is why fatigue management is critical in safety-sensitive industries.
API Recommended Practice 755 sets fatigue risk management guidelines for petroleum and chemical facilities. Key limits include a maximum of 16 hours in any 24-hour period, a maximum of 36 hours in any 48-hour period, a minimum of 8 hours rest between shifts, a maximum of 7 consecutive night shifts, and averaging no more than 60 hours per week over any 4-week period. These are guidelines rather than regulations, but most major refiners incorporate them into site policies.
Individual 12-hour shifts produce higher end-of-shift fatigue scores than 8-hour shifts. However, 12-hour rotation schedules typically include more days off (e.g., 4 on / 4 off vs 5 on / 2 off), which can provide better recovery. The net fatigue risk depends on the specific rotation pattern, night shift distribution, and transition frequency. Some studies show 12-hour schedules have equal or lower cumulative fatigue if the rotation is well-designed with adequate rest days.
Minimum rest requirements vary by regulatory framework. API RP 755 recommends at least 8 hours between shifts. The EU Working Time Directive requires 11 consecutive hours of rest in every 24-hour period. NRC 10 CFR 26 requires a minimum 10-hour break between shifts. FMCSA requires 10 consecutive hours off duty. From a fatigue science perspective, less than 11 hours between shifts does not allow adequate sleep opportunity because time must also be allocated for commuting, eating, and personal needs.
Cumulative fatigue builds progressively over consecutive work days, even when individual shifts are within normal length. Research shows measurable performance degradation after 5 to 7 consecutive days of work. Night shifts compound this effect because daytime sleep is typically shorter and of lower quality. Most fatigue management guidelines recommend no more than 5 to 7 consecutive shifts (especially nights) before a rest break of at least 48 hours.
Disclaimer: Fatigue risk scores are estimates based on biomathematical modeling and published research. They do not replace comprehensive fatigue risk management systems, medical evaluations, or regulatory compliance programs. Always consult applicable industry regulations and qualified occupational health professionals for fatigue management decisions.

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