Industrial Engineering Methods: Work Measurement, Methods Study, and Ergonomics
Industrial engineering methods test quantitative work measurement, methods study, and ergonomics. Expect standard time, performance rating, allowances, work sampling, predetermined motion times, method improvement, and ergonomic risk assessment.
Core rules
- Standard time = observed time × performance rating × (1 + allowance). Rate the pace first, then add allowances for personal needs, fatigue, and delay.
- Break work into measurable elements with clear start and stop points. Time enough cycles to control variation; note foreign elements separately.
- Work sampling estimates the proportion of time in an activity. Required sample size depends on desired confidence and precision; random observations are essential.
- Methods study uses eliminate, combine, rearrange, simplify. Improve the method before setting a standard.
- Ergonomics: assess posture, force, repetition, and recovery. The NIOSH lifting equation yields a recommended weight limit; RULA and REBA screen postural risk.
- Predetermined motion time systems use published motion times; 1 TMU equals 0.00001 hour, or 0.036 second.
Worked example
A task has an observed cycle of 8.0 minutes, a performance rating of 110 percent, and a 15 percent allowance. Normal time = 8.0 × 1.10 = 8.8 minutes. Standard time = 8.8 × 1.15 = 10.12 minutes. The reasoning is order-sensitive: applying the allowance to the observed time first would give 9.2 minutes, which incorrectly mixes pace and allowance. If the allowance were 18 percent, standard time would be 8.8 × 1.18 = 10.38 minutes.
Traps
- Adding allowances before applying the performance rating.
- Timing only the visible work and ignoring waiting, setup, or cleanup that belongs in the standard.
- Treating a screening tool such as RULA as a precise exposure limit.
- Setting a standard from a method that has not been standardized.