How Productive is Shift Work?
By John S. Mrowiec
When a construction project is delayed, the contractor might recover the time by employing overtime, increasing the manpower on a single shift or adding one or more additional shifts. A perceived benefit of shift work is that it might not cause the lost productivity resulting from fatigue caused by extended overtime or from the overmanning of increased manpower on a finite site.
Certainly, shift work involves a higher wage rate and, sometimes, employers pay for eight hours but employees work 7.5 hours. The “shift premium” could be 20%.
If the contractor did not cause the delay, many owners are willing to pay that shift premium. The owner and contractor might disagree about whether that represents the entirety of the additional cost.
Is shift work less productive than normal day work? Might shift work be even more productive than normal day work under some conditions?
In past columns, we attempted to summarize some of the published work of Dr. Awad Hanna, Professor of the Construction Engineering and Management Program and Chair of the Department of Civil and Environmental Engineering at the University of Wisconsin at Madison, regarding labor productivity impacts arising from acceleration, Discover the True Cost of Overtime and Shift Work Before Signing Accelerated Work Orders (February 2001) and Overtime, Project Duration and Labor Productivity (October 2005).
Quantifying Shift-Work Productivity
Hanna and others have published a new article proposing a method to quantify the productivity of shift work under particular parameters, Impact of Shift Work on Labor Productivity for Labor Intensive Contractor, 134:3 J. Constr. Eng. & Mgmn’t 197 (March 2008).
Hanna’s group surveyed the literature regarding shift work in construction and found little. He attributed the scarcity of studies to the fact that shift work is less common in the construction industry than in manufacturing or healthcare.
Those industries’ studies reported that the cost of shift work was normally higher than that of normal operation. Additional costs introduced by shift work included the need for more administrative personnel, supervision, quality control, safety and lighting in addition to the shift premium.
Yet few studies, even those that reported increased costs, attempted to measure the quantitative effects of shift work on labor performance and productivity.
Hanna’s research team collected construction project data from mechanical and sheet-metal contractors by survey. The researchers eventually created a data base with 26 projects suitable for study. The database includes projects from 15 states and five types of construction: commercial, industrial, institutional, residential and manufacturing.
Hanna used labor hours as the comparison base in order to combine the different types of projects into a single database. The projects ranged in manhours from 3,000 to 550,000.
Hanna attempted to measure the loss of efficiency as the difference between actual hours used and earned hours. The “earned hours” included approved manhours for change orders.
Hanna then established the ratio of shift work on a project by dividing the total shift work manhours by the budgeted total man-hours. The various projects in the database had ratios of .01 through .53 of shift work.
Hanna then performed regression analysis to develop the quantitative relationship between lost productivity and shift work. From the results, Hanna was able to develop an equation. From that equation, Hanna extrapolated a useful table showing the productivity multiplier for various percentages of shift work.
Productivity Up Only in Short Periods
Hanna’s results found that at 4% of shift work to budgeted hours, productivity was actually 11% more efficient. Thereafter, productivity declined as the percentage of shift work increased so that when shift hours were 50% of budgeted total hours, productivity had declined by 17%.
In attempting to validate the results, Hanna found that his equation seems to be more accurate for projects experiencing less than 20% total productivity losses. Hanna admits that the “relatively small sample size of contractors surveyed (26) means that the derived equation may be slightly skewed.”
Based on his study, Hanna concludes that shift work has positive effects that “make it a preferable option in place of overtime or over manning. However, the coordination problem it presents and health problems it could raise in the workers must also be considered when making the decision of how to accelerate the schedule.”
Hanna recommends shift work as an effective schedule compression technique in labor-intensive construction if it is used for a short duration.
Shift work can be effective in the situations where management is overlapped at the end of the prior shift and beginning of the next shift; where independent tasks are assigned to the shift work from the tasks performed by the previous shift; where shift work is employed only for a well-defined scope that does not require much engineering and design support; and where adequate materials and sufficient artificial lighting are provided for the later shift so congestion is avoided.
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