Supply Chain Efficiency vs
Supply Chain Efficiency vs. Effectiveness
- 1 Supply Chain Efficiency vs. Effectiveness
- 2 What is supply chain efficiency?
- 3 What is supply chain effectiveness?
- 4 Supply Chain Efficiency vs. Effectiveness
- 5 Why are supply chains sometimes efficient but not effective?
- 6 What can we learn?
- 7 probe
- 8 Definition of probe
- 9 Other Words from probe
- 10 Synonyms for probe
- 11 Choose the Right Synonym for probe
- 12 Examples of probe in a Sentence
- 13 First Known Use of probe
- 14 History and Etymology for probe
Supply chain managers at wholesale distribution and manufacturing companies might think that if a process is efficient, it is also effective. In fact, that may not always be the case. But how can a supply chain be efficient, yet not effective? It can happen when a company is more concerned with internal process improvements than the needs of its customers, stakeholders, or the supply chain as a whole. It can also happen because of the relationship between the two concepts. Efficiency and effectiveness are interrelated, yet independent. A supply chain therefore could be efficient and effective, neither efficient nor effective, efficient but not effective, or effective but not efficient. Confused? LetвЂ™s take a closer look at these concepts.
What is supply chain efficiency?
According to a white paper released by Industrial Marketing and Purchasing (IMP) Group, organizational efficiency is defined as an internal standard of performance. Supply chain efficiency is related to whether a companyвЂ™s processes are harnessing resources in the best way possible, whether those resources are financial, human, technological or physical. Notice that the definition of efficiency says nothing about improving customer service. You might have a very efficient supply chain that minimizes costs for materials and packaging but leaves your customers fuming when the product they receive is not up to their specifications. The term efficiency is also a very abstract one. People have different definitions, and againвЂ¦what may be deemed вЂњefficientвЂќ in one part of your supply chain may adversely affect another area of your business.
What is supply chain effectiveness?
The definition of effectiveness, on the other hand, is more externally focused on results. Organizational effectiveness is defined by IMP group as an external standard of how well an organization is meeting the demands of the various groups and organizations that are concerned with its activities. These groups might include customers, partners, suppliers and vendors. So, to measure your supply chain effectiveness, take a look at not just what is going on within the walls of your own company, but how this is ultimately impacting customers and the supply chain as a whole.
Supply Chain Efficiency vs. Effectiveness
When considering the efficiency or effectiveness of a supply chain, weвЂ™re evaluating each from different perspectives. When thinking about supply chain efficiency, weвЂ™re considering what happens within the supply chain system. The supply chain is efficient when we are able to get products at the lowest cost. We also might be looking at how well we are able to coordinate with others in our supply chain for extended manufacturing processes. When a supply chain is effective, weвЂ™re looking from outside the company. Customers are looking at whether they got the right product in the right timeframe to meet their needs. Stakeholders might be looking at how much revenue was generated relative to the cost. Vendors and other business partners might also be looking at how well we were able to solve problems.
Why are supply chains sometimes efficient but not effective?
Lora Cecere of Supply Chain Insights wrote in a recent Forbes article that while many companies believe supply chain efficiency and supply chain effectiveness to be one and the same, it is her firm belief after three years of research that, вЂњthe most efficient supply chain is not effective.вЂќ While she believes that improvements in supply chain technology have resulted in many process efficiencies for companies, they have not resulted in an overall reduction in costs to customers or improvements in margins for companies themselves. Her belief is based on studying results for publicly traded companies greater than $5 billion in annual revenue from 2000-2012. According to Cecere, вЂњYes, labor productivity improved; but, four out of eleven of the industries did not make progress on operating margins and inventory turns. And for many industries, the progress on labor productivity is much greater than the changes in operating margin and inventory turns.вЂќ Why is this happening? One reason is increased commodity costs and increased reliance on outsourcing. Companies have pushed costs to their supply chain partners, but this has not resulted in better results for customers on the measures they care about, such as on-time delivery and lower prices. A well-publicized case in point is The Boeing Company, whose recent foray into large-scale outsourcing of its manufacturing processes to its supply chain partners on its 787 Dreamliner program resulted in nearly three years of delays in delivering product to customers, and billions of dollars in cost overruns. Outsourcing is a common practice within highly complex industries such as aerospace and automotive, but this is typically out of necessityвЂ“вЂ“companies that make cars may not make radios, tires or other components, and aircraft manufacturers may not make engines or electronics. BoeingвЂ™s 787 supply chain strategy was envisioned not just as a necessity but as a way to be more competitive against its major rival, Airbus, by keeping manufacturing and assembly costs low while sharing risk with BoeingвЂ™s suppliers. Based on our definitions of supply chain efficiency vs supply chain effectiveness, this strategy was efficient in that it met internal company needs for a lean supply chain, yet not effective due to its negative impacts on customers and other stakeholders.
What can we learn?
So what can we learn from all this? That supply chain systems are extremely complex goes without saying. In general, it is very difficult to improve efficiency in meaningful ways, unless we look at both efficiency and effectiveness. We must look beyond our internal company requirements to how improvements in our processes will impact external partners and customers. In other words, not only must we do things right, we must also do the right things. Got an example of a supply chain that is both efficient and effective? Or a horror story about one that is neither? Let us know in the comments.
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Definition of probe
Definition of probe (Entry 2 of 2)
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Other Words from probe
Synonyms for probe
- delve (into),
- dig (into),
- inquire (into),
- look (into),
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Choose the Right Synonym for probe
enter, penetrate, pierce, probe mean to make way into something. enter is the most general of these and may imply either going in or forcing a way in. entered the city in triumph penetrate carries a strong implication of an impelling force or compelling power that achieves entrance. the enemy penetrated the fortress pierce means an entering or cutting through with a sharp pointed instrument. pierced the boil with a lancet probe implies penetration to investigate or explore something hidden from sight or knowledge. probed the depths of the sea
Examples of probe in a Sentence
These example sentences are selected automatically from various online news sources to reflect current usage of the word ‘probe.’ Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.
First Known Use of probe
1580, in the meaning defined at sense 1
circa 1543, in the meaning defined at sense 2
History and Etymology for probe
Medieval Latin proba examination, from Latin probare
13. Quality Control and Safety During Construction
Quality control and safety represent increasingly important concerns for project managers. Defects or failures in constructed facilities can result in very large costs. Even with minor defects, re-construction may be required and facility operations impaired. Increased costs and delays are the result. In the worst case, failures may cause personal injuries or fatalities. Accidents during the construction process can similarly result in personal injuries and large costs. Indirect costs of insurance, inspection and regulation are increasing rapidly due to these increased direct costs. Good project managers try to ensure that the job is done right the first time and that no major accidents occur on the project.
As with cost control, the most important decisions regarding the quality of a completed facility are made during the design and planning stages rather than during construction. It is during these preliminary stages that component configurations, material specifications and functional performance are decided. Quality control during construction consists largely of insuring conformance to these original design and planning decisions.
While conformance to existing design decisions is the primary focus of quality control, there are exceptions to this rule. First, unforeseen circumstances, incorrect design decisions or changes desired by an owner in the facility function may require re-evaluation of design decisions during the course of construction. While these changes may be motivated by the concern for quality, they represent occasions for re-design with all the attendant objectives and constraints. As a second case, some designs rely upon informed and appropriate decision making during the construction process itself. For example, some tunneling methods make decisions about the amount of shoring required at different locations based upon observation of soil conditions during the tunneling process. Since such decisions are based on better information concerning actual site conditions, the facility design may be more cost effective as a result. Any special case of re-design during construction requires the various considerations discussed in Chapter 3.
With the attention to conformance as the measure of quality during the construction process, the specification of quality requirements in the design and contract documentation becomes extremely important. Quality requirements should be clear and verifiable, so that all parties in the project can understand the requirements for conformance. Much of the discussion in this chapter relates to the development and the implications of different quality requirements for construction as well as the issues associated with insuring conformance.
Safety during the construction project is also influenced in large part by decisions made during the planning and design process. Some designs or construction plans are inherently difficult and dangerous to implement, whereas other, comparable plans may considerably reduce the possibility of accidents. For example, clear separation of traffic from construction zones during roadway rehabilitation can greatly reduce the possibility of accidental collisions. Beyond these design decisions, safety largely depends upon education, vigilance and cooperation during the construction process. Workers should be constantly alert to the possibilities of accidents and avoid taken unnecessary risks.
13.2 Organizing for Quality and Safety
A variety of different organizations are possible for quality and safety control during construction. One common model is to have a group responsible for quality assurance and another group primarily responsible for safety within an organization. In large organizations, departments dedicated to quality assurance and to safety might assign specific individuals to assume responsibility for these functions on particular projects. For smaller projects, the project manager or an assistant might assume these and other responsibilities. In either case, insuring safe and quality construction is a concern of the project manager in overall charge of the project in addition to the concerns of personnel, cost, time and other management issues.
Inspectors and quality assurance personnel will be involved in a project to represent a variety of different organizations. Each of the parties directly concerned with the project may have their own quality and safety inspectors, including the owner, the engineer/architect, and the various constructor firms. These inspectors may be contractors from specialized quality assurance organizations. In addition to on-site inspections, samples of materials will commonly be tested by specialized laboratories to insure compliance. Inspectors to insure compliance with regulatory requirements will also be involved. Common examples are inspectors for the local government’s building department, for environmental agencies, and for occupational health and safety agencies.
The US Occupational Safety and Health Administration (OSHA) routinely conducts site visits of work places in conjunction with approved state inspection agencies. OSHA inspectors are required by law to issue citations for all standard violations observed. Safety standards prescribe a variety of mechanical safeguards and procedures; for example, ladder safety is covered by over 140 regulations. In cases of extreme non-compliance with standards, OSHA inspectors can stop work on a project. However, only a small fraction of construction sites are visited by OSHA inspectors and most construction site accidents are not caused by violations of existing standards. As a result, safety is largely the responsibility of the managers on site rather than that of public inspectors.
While the multitude of participants involved in the construction process require the services of inspectors, it cannot be emphasized too strongly that inspectors are only a formal check on quality control. Quality control should be a primary objective for all the members of a project team. Managers should take responsibility for maintaining and improving quality control. Employee participation in quality control should be sought and rewarded, including the introduction of new ideas. Most important of all, quality improvement can serve as a catalyst for improved productivity. By suggesting new work methods, by avoiding rework, and by avoiding long term problems, good quality control can pay for itself. Owners should promote good quality control and seek out contractors who maintain such standards.
In addition to the various organizational bodies involved in quality control, issues of quality control arise in virtually all the functional areas of construction activities. For example, insuring accurate and useful information is an important part of maintaining quality performance. Other aspects of quality control include document control (including changes during the construction process), procurement, field inspection and testing, and final checkout of the facility.
13.3 Work and Material Specifications
Specifications of work quality are an important feature of facility designs. Specifications of required quality and components represent part of the necessary documentation to describe a facility. Typically, this documentation includes any special provisions of the facility design as well as references to generally accepted specifications to be used during construction.
General specifications of work quality are available in numerous fields and are issued in publications of organizations such as the American Society for Testing and Materials (ASTM), the American National Standards Institute (ANSI), or the Construction Specifications Institute (CSI). Distinct specifications are formalized for particular types of construction activities, such as welding standards issued by the American Welding Society, or for particular facility types, such as the Standard Specifications for Highway Bridges issued by the American Association of State Highway and Transportation Officials. These general specifications must be modified to reflect local conditions, policies, available materials, local regulations and other special circumstances.
Construction specifications normally consist of a series of instructions or prohibitions for specific operations. For example, the following passage illustrates a typical specification, in this case for excavation for structures:
Conform to elevations and dimensions shown on plan within a tolerance of plus or minus 0.10 foot, and extending a sufficient distance from footings and foundations to permit placing and removal of concrete formwork, installation of services, other construction, and for inspection. In excavating for footings and foundations, take care not to disturb bottom of excavation. Excavate by hand to final grade just before concrete reinforcement is placed. Trim bottoms to required lines and grades to leave solid base to receive concrete.
This set of specifications requires judgment in application since some items are not precisely specified. For example, excavation must extend a «sufficient» distance to permit inspection and other activities. Obviously, the term «sufficient» in this case may be subject to varying interpretations. In contrast, a specification that tolerances are within plus or minus a tenth of a foot is subject to direct measurement. However, specific requirements of the facility or characteristics of the site may make the standard tolerance of a tenth of a foot inappropriate. Writing specifications typically requires a trade-off between assuming reasonable behavior on the part of all the parties concerned in interpreting words such as «sufficient» versus the effort and possible inaccuracy in pre-specifying all operations.
In recent years, performance specifications have been developed for many construction operations. Rather than specifying the required construction process, these specifications refer to the required performance or quality of the finished facility. The exact method by which this performance is obtained is left to the construction contractor. For example, traditional specifications for asphalt pavement specified the composition of the asphalt material, the asphalt temperature during paving, and compacting procedures. In contrast, a performance specification for asphalt would detail the desired performance of the pavement with respect to impermeability, strength, etc. How the desired performance level was attained would be up to the paving contractor. In some cases, the payment for asphalt paving might increase with better quality of asphalt beyond some minimum level of performance.
Example 13-1: Concrete Pavement Strength
Concrete pavements of superior strength result in cost savings by delaying the time at which repairs or re-construction is required. In contrast, concrete of lower quality will necessitate more frequent overlays or other repair procedures. Contract provisions with adjustments to the amount of a contractor’s compensation based on pavement quality have become increasingly common in recognition of the cost savings associated with higher quality construction. Even if a pavement does not meet the «ultimate» design standard, it is still worth using the lower quality pavement and re-surfacing later rather than completely rejecting the pavement. Based on these life cycle cost considerations, a typical pay schedule might be: 
|Load Ratio||Pay Factor|
The function g(p) indicates the probability of accepting a lot, given the sample size n and the number of allowable defective items in the sample r. The function g(p) can be represented graphical for each combination of sample size n and number of allowable defective items r, as shown in Figure 13-1. Each curve is referred to as the operating characteristic curve (OC curve) in this graph. For the special case of a single sample (n=1), the function g(p) can be simplified:
so that the probability of accepting a lot is equal to the fraction of acceptable items in the lot. For example, there is a probability of 0.5 that the lot may be accepted from a single sample test even if fifty percent of the lot is defective.
Figure 13-1 Example Operating Characteristic Curves Indicating Probability of Lot Acceptance
For any combination of n and r, we can read off the value of g(p) for a given p from the corresponding OC curve. For example, n = 15 is specified in Figure 13-1. Then, for various values of r, we find:
The producer’s and consumer’s risk can be related to various points on an operating characteristic curve. Producer’s risk is the chance that otherwise acceptable lots fail the sampling plan (ie. have more than the allowable number of defective items in the sample) solely due to random fluctuations in the selection of the sample. In contrast, consumer’s risk is the chance that an unacceptable lot is acceptable (ie. has less than the allowable number of defective items in the sample) due to a better than average quality in the sample. For example, suppose that a sample size of 15 is chosen with a trigger level for rejection of one item. With a four percent acceptable level and a greater than four percent defective fraction, the consumer’s risk is at most eighty-eight percent. In contrast, with a four percent acceptable level and a four percent defective fraction, the producer’s risk is at most 1 — 0.88 = 0.12 or twelve percent.
In specifying the sampling plan implicit in the operating characteristic curve, the supplier and consumer of materials or work must agree on the levels of risk acceptable to themselves. If the lot is of acceptable quality, the supplier would like to minimize the chance or risk that a lot is rejected solely on the basis of a lower than average quality sample. Similarly, the consumer would like to minimize the risk of accepting under the sampling plan a deficient lot. In addition, both parties presumably would like to minimize the costs and delays associated with testing. Devising an acceptable sampling plan requires trade off the objectives of risk minimization among the parties involved and the cost of testing.
Example 13-3: Acceptance probability calculation
Suppose that the sample size is five (n=5) from a lot of one hundred items (N=100). The lot of materials is to be rejected if any of the five samples is defective (r = 0). In this case, the probability of acceptance as a function of the actual number of defective items can be computed by noting that for r = 0, only one term (x = 0) need be considered in Eq. (13.4). Thus, for N = 100 and n = 5:
For a two percent defective fraction (p = 0.02), the resulting acceptance value is:
Using the binomial approximation in Eq. (13.5), the comparable calculation would be:
which is a difference of 0.0019, or 0.21 percent from the actual value of 0.9020 found above.
If the acceptable defective proportion was two percent (so p 1 = p 2 = 0.02), then the chance of an incorrect rejection (or producer’s risk) is 1 — g(0.02) = 1 — 0.9 = 0.1 or ten percent. Note that a prudent producer should insure better than minimum quality products to reduce the probability or chance of rejection under this sampling plan. If the actual proportion of defectives was one percent, then the producer’s risk would be only five percent with this sampling plan.
Example 13-4: Designing a Sampling Plan
Suppose that an owner (or product «consumer» in the terminology of quality control) wishes to have zero defective items in a facility with 5,000 items of a particular kind. What would be the different amounts of consumer’s risk for different sampling plans?
With an acceptable quality level of no defective items (so p 1 = 0), the allowable defective items in the sample is zero (so r = 0) in the sampling plan. Using the binomial approximation, the probability of accepting the 5,000 items as a function of the fraction of actual defective items and the sample size is:
To insure a ninety percent chance of rejecting a lot with an actual percentage defective of one percent (p = 0.01), the required sample size would be calculated as:
As can be seen, large sample sizes are required to insure relatively large probabilities of zero defective items.
13.7 Statistical Quality Control with Sampling by Variables
As described in the previous section, sampling by attributes is based on a classification of items as good or defective . Many work and material attributes possess continuous properties, such as strength, density or length. With the sampling by attributes procedure, a particular level of a variable quantity must be defined as acceptable quality. More generally, two items classified as good might have quite different strengths or other attributes. Intuitively, it seems reasonable that some «credit» should be provided for exceptionally good items in a sample. Sampling by variables was developed for application to continuously measurable quantities of this type. The procedure uses measured values of an attribute in a sample to determine the overall acceptability of a batch or lot. Sampling by variables has the advantage of using more information from tests since it is based on actual measured values rather than a simple classification. As a result, acceptance sampling by variables can be more efficient than sampling by attributes in the sense that fewer samples are required to obtain a desired level of quality control.
In applying sampling by variables, an acceptable lot quality can be defined with respect to an upper limit U, a lower limit L, or both. With these boundary conditions, an acceptable quality level can be defined as a maximum allowable fraction of defective items, M. In Figure 13-2, the probability distribution of item attribute x is illustrated. With an upper limit U, the fraction of defective items is equal to the area under the distribution function to the right of U (so that x U). This fraction of defective items would be compared to the allowable fraction M to determine the acceptability of a lot. With both a lower and an upper limit on acceptable quality, the fraction defective would be the fraction of items greater than the upper limit or less than the lower limit. Alternatively, the limits could be imposed upon the acceptable average level of the variable
Figure 13-2 Variable Probability Distributions and Acceptance Regions
In sampling by variables, the fraction of defective items is estimated by using measured values from a sample of items. As with sampling by attributes, the procedure assumes a random sample of a give size is obtained from a lot or batch. In the application of sampling by variables plans, the measured characteristic is virtually always assumed to be normally distributed as illustrated in Figure 13-2. The normal distribution is likely to be a reasonably good assumption for many measured characteristics such as material density or degree of soil compaction. The Central Limit Theorem provides a general support for the assumption: if the source of variations is a large number of small and independent random effects, then the resulting distribution of values will approximate the normal distribution. If the distribution of measured values is not likely to be approximately normal, then sampling by attributes should be adopted. Deviations from normal distributions may appear as skewed or non-symmetric distributions, or as distributions with fixed upper and lower limits.
The fraction of defective items in a sample or the chance that the population average has different values is estimated from two statistics obtained from the sample: the sample mean and standard deviation. Mathematically, let n be the number of items in the sample and x i , i = 1,2,3. n, be the measured values of the variable characteristic x. Then an estimate of the overall population mean is the sample mean :
An estimate of the population standard deviation is s, the square root of the sample variance statistic:
Based on these two estimated parameters and the desired limits, the various fractions of interest for the population can be calculated.
The probability that the average value of a population is greater than a particular lower limit is calculated from the test statistic:
which is t-distributed with n-1 degrees of freedom. If the population standard deviation is known in advance, then this known value is substituted for the estimate s and the resulting test statistic would be normally distributed. The t distribution is similar in appearance to a standard normal distribution, although the spread or variability in the function decreases as the degrees of freedom parameter increases . As the number of degrees of freedom becomes very large, the t-distribution coincides with the normal distribution.
With an upper limit, the calculations are similar, and the probability that the average value of a population is less than a particular upper limit can be calculated from the test statistic:
With both upper and lower limits, the sum of the probabilities of being above the upper limit or below the lower limit can be calculated.
The calculations to estimate the fraction of items above an upper limit or below a lower limit are very similar to those for the population average. The only difference is that the square root of the number of samples does not appear in the test statistic formulas:
where t AL is the test statistic for all items with a lower limit and t AU is the test statistic for all items with a upper limit. For example, the test statistic for items above an upper limit of 5.5 with = 4.0, s = 3.0, and n = 5 is t AU = (8.5 — 4.0)/3.0 = 1.5 with n — 1 = 4 degrees of freedom.
Instead of using sampling plans that specify an allowable fraction of defective items, it saves computations to simply write specifications in terms of the allowable test statistic values themselves. This procedure is equivalent to requiring that the sample average be at least a pre-specified number of standard deviations away from an upper or lower limit. For example, with = 4.0, U = 8.5, s = 3.0 and n = 41, the sample mean is only about (8.5 — 4.0)/3.0 = 1.5 standard deviations away from the upper limit.
To summarize, the application of sampling by variables requires the specification of a sample size, the relevant upper or limits, and either (1) the allowable fraction of items falling outside the designated limits or (2) the allowable probability that the population average falls outside the designated limit. Random samples are drawn from a pre-defined population and tested to obtained measured values of a variable attribute. From these measurements, the sample mean, standard deviation, and quality control test statistic are calculated. Finally, the test statistic is compared to the allowable trigger level and the lot is either accepted or rejected. It is also possible to apply sequential sampling in this procedure, so that a batch may be subjected to additional sampling and testing to further refine the test statistic values.
With sampling by variables, it is notable that a producer of material or work can adopt two general strategies for meeting the required specifications. First, a producer may insure that the average quality level is quite high, even if the variability among items is high. This strategy is illustrated in Figure 13-3 as a «high quality average» strategy. Second, a producer may meet a desired quality target by reducing the variability within each batch. In Figure 13-3, this is labeled the «low variability» strategy. In either case, a producer should maintain high standards to avoid rejection of a batch.
Figure 13-3 Testing for Defective Component Strengths
Example 13-5: Testing for defective component strengths
Suppose that an inspector takes eight strength measurements with the following results:
4.3, 4.8, 4.6, 4.7, 4.4, 4.6, 4.7, 4.6
In this case, the sample mean and standard deviation can be calculated using Equations (13.8) and (13.9):
= 1/8(4.3 + 4.8 + 4.6 + 4.7 + 4.4 + 4.6 + 4.7 + 4.6) = 4.59
s 2 =[1/(8-1)][(4.3 — 4.59) 2 + (4.8 — 4.59) 2 + (4.6 — 4.59) 2 + (4.7 — 4.59) 2 + (4.4 — 4.59) 2 + (4.6 — 4.59) 2 + (4.7 — 4.59) 2 + (4.6 — 4.59) 2 ] = 0.16
The percentage of items below a lower quality limit of L = 4.3 is estimated from the test statistic t AL in Equation (13.12):
Construction is a relatively hazardous undertaking. As Table 13-1 illustrates, there are significantly more injuries and lost workdays due to injuries or illnesses in construction than in virtually any other industry. These work related injuries and illnesses are exceedingly costly. The Construction Industry Cost Effectiveness Project estimated that accidents cost $8.9 billion or nearly seven percent of the $137 billion (in 1979 dollars) spent annually for industrial, utility and commercial construction in the United States.  Included in this total are direct costs (medical costs, premiums for workers’ compensation benefits, liability and property losses) as well as indirect costs (reduced worker productivity, delays in projects, administrative time, and damage to equipment and the facility). In contrast to most industrial accidents, innocent bystanders may also be injuried by construction accidents. Several crane collapses from high rise buildings under construction have resulted in fatalities to passerbys. Prudent project managers and owners would like to reduce accidents, injuries and illnesses as much as possible.
|Note: Data represent total number of cases per 100 full-time employees|
|Source: U.S. Bureau of Labor Statistics, Occupational injuries and Illnesses in the United States by Industry , annual|
As with all the other costs of construction, it is a mistake for owners to ignore a significant category of costs such as injury and illnesses. While contractors may pay insurance premiums directly, these costs are reflected in bid prices or contract amounts. Delays caused by injuries and illnesses can present significant opportunity costs to owners. In the long run, the owners of constructed facilities must pay all the costs of construction. For the case of injuries and illnesses, this general principle might be slightly qualified since significant costs are borne by workers themselves or society at large. However, court judgements and insurance payments compensate for individual losses and are ultimately borne by the owners.
The causes of injuries in construction are numerous. Table 13-2 lists the reported causes of accidents in the US construction industry in 1997 and 2004. A similar catalogue of causes would exist for other countries. The largest single category for both injuries and fatalities are individual falls. Handling goods and transportation are also a significant cause of injuries. From a management perspective, however, these reported causes do not really provide a useful prescription for safety policies. An individual fall may be caused by a series of coincidences: a railing might not be secure, a worker might be inattentive, the footing may be slippery, etc. Removing any one of these compound causes might serve to prevent any particular accident. However, it is clear that conditions such as unsecured railings will normally increase the risk of accidents. Table 13-3 provides a more detailed list of causes of fatalities for construction sites alone, but again each fatality may have multiple causes.
Various measures are available to improve jobsite safety in construction. Several of the most important occur before construction is undertaken. These include design, choice of technology and education. By altering facility designs, particular structures can be safer or more hazardous to construct. For example, parapets can be designed to appropriate heights for construction worker safety, rather than the minimum height required by building codes.
Choice of technology can also be critical in determining the safety of a jobsite. Safeguards built into machinery can notify operators of problems or prevent injuries. For example, simple switches can prevent equipment from being operating when protective shields are not in place. With the availability of on-board electronics (including computer chips) and sensors, the possibilities for sophisticated machine controllers and monitors has greatly expanded for construction equipment and tools. Materials and work process choices also influence the safety of construction. For example, substitution of alternative materials for asbestos can reduce or eliminate the prospects of long term illnesses such as asbestiosis .
Educating workers and managers in proper procedures and hazards can have a direct impact on jobsite safety. The realization of the large costs involved in construction injuries and illnesses provides a considerable motivation for awareness and education. Regular safety inspections and safety meetings have become standard practices on most job sites.
Pre-qualification of contractors and sub-contractors with regard to safety is another important avenue for safety improvement. If contractors are only invitied to bid or enter negotiations if they have an acceptable record of safety (as well as quality performance), then a direct incentive is provided to insure adequate safety on the part of contractors.
During the construction process itself, the most important safety related measures are to insure vigilance and cooperation on the part of managers, inspectors and workers. Vigilance involves considering the risks of different working practices. In also involves maintaining temporary physical safeguards such as barricades, braces, guylines, railings, toeboards and the like. Sets of standard practices are also important, such as: 
- requiring hard hats on site.
- requiring eye protection on site.
- requiring hearing protection near loud equipment.
- insuring safety shoes for workers.
- providing first-aid supplies and trained personnel on site
While eliminating accidents and work related illnesses is a worthwhile goal, it will never be attained. Construction has a number of characteristics making it inherently hazardous. Large forces are involved in many operations. The jobsite is continually changing as construction proceeds. Workers do not have fixed worksites and must move around a structure under construction. The tenure of a worker on a site is short, so the worker’s familiarity and the employer-employee relationship are less settled than in manufacturing settings. Despite these peculiarities and as a result of exactly these special problems, improving worksite safety is a very important project management concern.
Example 13-6: Trench collapse 
To replace 1,200 feet of a sewer line, a trench of between 12.5 and 18 feet deep was required down the center of a four lane street. The contractor chose to begin excavation of the trench from the shallower end, requiring a 12.5 deep trench. Initially, the contractor used a nine foot high, four foot wide steel trench box for soil support. A trench box is a rigid steel frame consisting of two walls supported by welded struts with open sides and ends. This method had the advantage that traffic could be maintained in at least two lanes during the reconstruction work.
In the shallow parts of the trench, the trench box seemed to adequately support the excavation. However, as the trench got deeper, more soil was unsupported below the trench box. Intermittent soil collapses in the trench began to occur. Eventually, an old parallel six inch water main collapsed, thereby saturating the soil and leading to massive soil collapse at the bottom of the trench. Replacement of the water main was added to the initial contract. At this point, the contractor began sloping the sides of the trench, thereby requiring the closure of the entire street.
The initial use of the trench box was convenient, but it was clearly inadequate and unsafe. Workers in the trench were in continuing danger of accidents stemming from soil collapse. Disruption to surrounding facilities such as the parallel water main was highly likely. Adoption of a tongue and groove vertical sheeting system over the full height of the trench or, alternatively, the sloping excavation eventually adopted are clearly preferable.
- Ang, A.H.S. and W.H. Tang, Probability Concepts in Engineering Planning and Design: Volume I — Basic Principles , John Wiley and Sons, Inc., New York, 1975.
- Au, T., R.M. Shane, and L.A. Hoel, Fundamentals of Systems Engineering: Probabilistic Models , Addison-Wesley Publishing Co., Reading MA, 1972
- Bowker, A.H. and Liebermann, G. J., Engineering Statistics , Prentice-Hall, 1972.
- Fox, A.J. and Cornell, H.A., (eds), Quality in the Constructed Project, American Society of Civil Engineers, New York, 1984.
- International Organization for Standardization, «Sampling Procedures and Charts for Inspection by Variables for Percent Defective, ISO 3951-1981 (E)», Statistical Methods , ISO Standard Handbook 3, International Organization for Standardization, Paris, France, 1981.
- Skibniewski, M. and Hendrickson, C., Methods to Improve the Safety Performance of the U.S. Construction Industry, Technical Report, Department of Civil Engineering, Carnegie Mellon University, 1983.
- United States Department of Defense, Sampling Procedures and Tables for Inspection by Variables , (Military Standard 414), Washington D.C.: U.S. Government Printing Office, 1957.
- United States Department of Defense, Sampling Procedures and Tables for Inspection by Attributes , (Military Standard 105D), Washington D.C.: U.S. Government Printing Office, 1963.
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- Consider the following specification. Would you consider it to be a process or performance specification? Why?
«Water used in mixing or curing shall be reasonably clean and free of oil, salt, acid, alkali, sugar, vegetable, or other substance injurious to the finished product. Water known to be potable quality may be used without test. Where the source of water is relatively shallow, the intake shall be so enclosed as to exclude silt, mud, grass, or other foreign materials.» 
Suppose that a sampling plan calls for a sample of size n = 50. To be acceptable, only three or fewer samples can be defective. Estimate the probability of accepting the lot if the average defective percentage is (a) 15%, (b) 5% or (c) 2%. Do not use an approximation in this calculation.
Repeat Problem 2 using the binomial approximation.
Suppose that a project manager tested the strength of one tile out of a batch of 3,000 to be used on a building. This one sample measurement was compared with the design specification and, in this case, the sampled tile’s strength exceeded that of the specification. On this basis, the project manager accepted the tile shipment. If the sampled tile was defective (with a strength less than the specification), the project manager would have rejected the lot.
a. What is the probability that ninety percent of the tiles are substandard, even though the project manager’s sample gave a satisfactory result?
b. Sketch out the operating characteristic curve for this sampling plan as a function of the actual fraction of defective tiles.
Repeat Problem 4 for sample sizes of (a) 5, (b) 10 and (c) 20.
Suppose that a sampling-by-attributes plan is specified in which ten samples are taken at random from a large lot (N=100) and at most one sample item is allowed to be defective for the lot to be acceptable.
a. If the actual percentage defective is five percent, what is the probability of lot acceptance? (Note: you may use relevant approximations in this calculation.)
b. What is the consumer’s risk if an acceptable quality level is fifteen percent defective and the actual fraction defective is five percent?
c. What is the producer’s risk with this sampling plan and an eight percent defective percentage?
a. What is the probability that the population mean is less than 50,000 psi?
b. What is the estimated fraction of pieces with yield strength less than 50,000 psi?
c. Is this sampling procedure sampling-by-attributes or sampling-by-variable?
a. If the actual percentage defective is five percent, what is the probability of lot acceptance? (Note: you may use relevant approximations in this calculation).
b. What is the consumer’s risk if an acceptable quality level is fifteen percent defective and the actual fraction defective is 0.05?
c. What is the producer’s risk with this sampling plan and a 8% defective percentage?
1. This illustrative pay factor schedule is adapted from R.M. Weed, «Development of Multicharacteristic Acceptance Procedures for Rigid Pavement,» Transportation Research Record 885 , 1982, pp. 25-36. Back
2. B.A. Gilly, A. Touran, and T. Asai, «Quality Control Circles in Construction,» ASCE Journal of Construction Engineering and Management , Vol. 113, No. 3, 1987, pg 432. Back
3. See Improving Construction Safety Performance , Report A-3, The Business Roundtable, New York, NY, January 1982. Back
4. Hinze, Jimmie W., Construction Safety, , Prentice-Hall, 1997. Back
5. This example was adapted from E. Elinski, External Impacts of Reconstruction and Rehabilitation Projects with Implications for Project Management, Unpublished MS Thesis, Department of Civil Engineering, Carnegie Mellon University, 1985. Back