6.2 Industrial engineering applications
6.2.1 Ergonomics/human factors
The study and redesign of construction workspace using traditional and modern IE tools could increase efficiency and minimize on-the-job injuries and worker health impacts.
Unlike factories, construction workspace constantly changes in geometry, size, location and type of material, location of work, location of material handling equipment and other tools, etc. These create new and challenging research opportunities. In addition, significant environmental impacts result from construction-related activities. Safety engineering approaches and industrial ecology tools such as life-cycle analysis may be developed to define and measure the impacts of different designs for workspaces and constructions.
Construction workers use a wide assortment of tools and equipment to perform con- struction tasks. Especially in cases where such aids are used for prolonged periods of time, workers’ effectiveness and capacity to work with high levels of concentration, ergonom- ics are a major concern. Workers cannot be expected to “build in” quality in constructed facilities if they are subjected to awkward positions and excessive physical stress caused by tools and equipment that are difficult to use.
The significance of ergonomics in the construction environment is evident from a study conducted by the Associated General Contractors (AGC) of California to examine ergonomics-related costs. Their findings are:
• Related Workers Comp Insurance claims had increased by up to 40% for many con- struction companies.
• Financial returns due to ergonomic business strategy—80% of the companies that had incorporated ergonomics-based methods reported improvements.
• Of 24 companies that measured for productivity, 100% reported improvements in cases where ergonomics-related concerns were addressed.
6.2.1.1 Tool and equipment design
Much research has yet to be done in the design of construction-oriented tools and equip- ment. The factors that may cause fatigue include weight, size, vibration, and operating temperature. Work-related musculoskeletal disorders (WRMSDs) generally include strains, sprains, soft tissue, and nerve injuries; they are cumulative trauma disorders and repetitive motion injuries. The construction workers who are at highest risk for these dis- orders are carpenters, plumbers, drywall installers, roofers, electricians, structural metal workers, carpet layers, tile setters, plasterers, and machine operators.
The top five contributory risk factors are as follows:
Working in a specific posture for prolonged periods, bending or rotating the trunk awkwardly, working in cramped or awkward positions, working after sustaining an injury, and handling heavy materials or equipment.
The use of a shovel is a very typical example of the labor-intensive material handling activities that are routinely carried out on construction projects. This activity requires workers to bend over, apply force to a shovel in different planes, and rotate the trunk in a flexed position. Such movements impose biomechanical stress which may impose cumu- lative trauma risk. Freivalds (1986) studied the work physiology of shoveling tasks and identified the shovel design parameters that would increase task efficiency. Friedvald’s two-phase experimental study addressed the following parameters:
• The size and shape of the shovel blade
• The lift angle
• Shovel contours—hollow and closed-back design
• Handle length
• Energy expenditure
• Perceived exertion
• Low-back compressive forces
The recommended shovel design is as follows:
• A lift angle of approximately 32°
• A hollow-back construction to reduce weight
• A long tapered handle
• A solid socket for strength in heavy-duty uses
• A large, square point blade for shoveling
• A round, point blade for digging, with a built-in step for digging in hard soil 6.2.1.2 Ergonomics applications in structural ironwork
The BLS reports that construction trade workers experience higher rates of musculoskel- etal injuries and disorders than workers in other industries: 7.9 cases per 100 equivalent workers as compared with the industry average of 5.7 per 100 (Bureau of Labor Statistics, 2001). In overall injuries, construction workers registered 7.8 vs. the industry average of 5.4. Observations by Holstrom et al. (1993), Guo et al. (1995), Kisner and Fosbroke (1994), and others point to a lack of studies in ergonomics, presumably because of high task vari- ability, irregular work periods, changing work environments, and the transient nature of construction trades. As pointed out by Forde and Buchholz (2004), each construction trade and task represents a unique situation; the identification and application of preven- tion measures, tools and work conditions is best derived from trade and task-specific studies. This approach is the most likely to minimize the incidence of construction trades’
WRMSDs.
By way of illustration, Forde and Buchholz (2004) studied construction ironworkers to identify mitigating measures in that group. Construction ironwork refers to outdoor work (not shop fabrication) as four specialties—the erection of structural steel (structural ironwork [SIW]), placement of reinforcing bars (rebars) (reinforcing ironwork [RIW]), orna- mental ironwork (OIW), and machinery moving and rigging (MMRIW).
Previous studies determined that construction ironwork involves lifting, carrying and manipulating of heavy loads, maintaining awkward postures in cramped quarters, work- ing with arms overhead for extended periods, using heavy, vibrating pneumatic tools, and extensive outdoor exposure in temperature and weather extremes.
Forde and Buchholz (2004) made the following observations and recommendations on the various categories of ironwork:
• Machinery moving/rigging. The erection of equipment such as a crane involves the pushing and pulling of large and heavy segments, and lining them up for bolting together. During an 8-h shift, this activity was observed to require 1.3 h of significant whole-body exertion. Workers in this scenario are most susceptible to overexertion of the back, legs, and shoulders.
105 Chapter six: Industrial engineering applications in the construction industry
• Ornamental ironwork. This work was observed to require arms to be above the shoul- der level 21% of the time. Trunk flexion or twisting and side bending were observed 23% of the time.
These percentages indicate a high risk of overexertion of the involved muscle groups.
Industrial engineers should review the work methods to increase the amount of preas- sembly at workbench height.
• Reinforcing ironwork. The preparation of reinforcement cages and tying of rebars were seen to cause nonneutral trunk postures up to 50% of the time. The handling of heavy loads (50 lb or greater) was observed to occur for 1.9 h of an 8-h shift, repre- senting significant long-term risk. A 2004 study by Forde and Buchholz identified a need to improve the design of hand tools used for securing rebars. Such redesign would reduce nonneutral hand/wrist postures such as flexion, extension, and radial and ulnar deviation. These postures put construction workers at risk of repetitive motion injuries.
6.2.1.3 Auxiliary handling devices
A number of research studies have shown that construction workers have suffered back, leg, and shoulder injuries because of overexertion resulting from stooped postures, per- forming manual tasks above shoulder level, and the lifting of heavy objects. Such overexer- tion and injuries reduce worker productivity and may negatively affect the timeliness and profitability of construction projects. The use of auxiliary handling devices may reduce the degree of overexertion experienced by construction workers, and enhance productivity.
Sillanpaa et al. (1999) studied the following five auxiliary devices:
• Carpet wheels
• A lifting strap for drain pipes
• A portable cutting bench for molding
• A portable storage rack
• A portable cutting bench for rebars.
The survey subjects utilized these devices to carry out typical construction tasks, such as carrying rolls of carpet, mounting drain pipes, cut pieces of molding, and fashioned rebars. The results of the study were mostly positive but mixed, pointing to the need for further research. The auxiliary devices were found to reduce the muscular load of some subjects, but others experienced an increased load because of differences in anthropomet- ric dimensions, work modes, and level of work experience.
6.2.1.4 Drywall hanging methods
Drywall lifting and hanging are extensively conducted in both residential and commercial building construction; drywall board has become the standard for interior wall panels. It is the standard for surfacing residential ceilings. Workers are required to handle heavy and bulky drywall sheets and assume and maintain awkward postures in the course of perform- ing installation work. These activities often cause muscle fatigue and lead to a loss of bal- ance; studies have identified drywall lifting and hanging tasks as causing more fall-related injuries than any other tasks. Pan et al. (2000) studied 60 construction workers to identify the methods resulting in the least postural stability during drywall lifting and hanging tasks.
The subjects’ instability was measured using a piezoelectric-type force platform.
Subjects’ propensity for loss of balance was described by two postural-sway variables (sway length and sway area) and three instability indices (PSB, SAR, and WRTI). The study was a randomized repeated design with lifting and hanging methods for lifting and hang- ing randomly assigned to the subjects. ANOVA indicated that the respective lifting and hanging methods had significant effects on two postural-sway variables and the three postural instability indices.
The recommended methods were:
• Lifting drywall sheets horizontally with both hands positioned on the top of the drywall causes the least postural sway and instability.
• Hanging drywall horizontally on ceilings produces less postural sway and instabil- ity than vertically.