Crash time

If all the activities were crashed, the project cost would be 66,350. However, not all the activities need to be crashed to complete the project in the crash time. 

To prove this, the crash time and minimum crash cost will now be determined. A cost-versus-completion-time curve will also be constructed. This curve increases the project manager s decision possibilities from two to many. With it he can determine whether it is most economical to get the job done as fast as possible, to proceed at a normal pace, or to choose some intermediate time. 

Optimal Change in Going from Normal to Crash Times for the Activities Given in Table 13-2... 

Code Activity Normal Time (days) Cost ( ) Crash Time (days) Crash cost ( ) Cost Slope /day... 

Activity Activity Number Expected Time Total Allowable Crash Time Normal Cost ( ) Crashed Cost Per Cost ( ) Day To Crash ( ) ... 

The pre-crash time, which is the timespan that remains from the start of the avoiding manoeuvre to the occurrence of the crash, provided that the road user (driver, etc.) had continued with unchanged speed and direction. 

An actual problem of a paper mill was the continuous measurement of the wall thickness of a heated roll which dries the paper in order to avoid severe crashes due to wearing. On one side the roll shall be used as long as possible because of economic aspects and on the other side the roll has to be replaced in time to avoid a severe crash. 

In 1942 the Japanese overran Malaya and the then Dutch East Indies to cut off the main sources of natural rubber for the United States and the British Commonwealth. Because of this the US Government initiated a crash programme for the installation of plants for the manufacture of a rubber from butadiene and styrene. This product, then known as GR-S (Government Rubber-Styrene), provided at that time an inferior substitute for natural rubber but, with a renewed availability of natural rubber at the end of the war, the demand for GR-S slumped considerably. (Today the demand for SBR (as GR-S is now known) has increased with the great improvements in quality that have been made and SBR is today the principal synthetic rubber). 

Appendix HI, of WASH-1400 presents a database from 52 references that were used in the study. It includes raw data, notes on test and maintenance time and frequency, human-reliability estimates, aircraft-crash probabilities, frequency of initiating events, and information on common-cause failures. Using this information, it assesses the range for each failure rate. 

Appendix III contains failure rate estimates for various genetic types of mechanical and electrical equipment. Included ate listings of failure rates with range estimates for specified component failure modes, demand probabilities, and times to maintain repair. It also contains some discussion on such special topics as human errors, aircraft crash probabilities, loss of electric power, and pipe breaks. Appendix III contains a great deal of general information of use to analysts on the methodology of data assessment for PRA. 

Blood alcohol concentration and risk of crash. With increasing alcohol concentration in the blood, the risk of an automobile crash rises rapidly to 25 times the normal risk of a crash (that is, the risk with no alcohol consumption). 

In the past when car crashworthiness was designed entirely experimentally, full-sized prototypes were subjected to the crash scenarios required by the relevant authorities. If the performance was unacceptable, the shape deformations of the components making up the prototype were examined. A new prototype was engineered empirically to overcome the identified weaknesses before being built and then destroyed in a subsequent test. These tests would be repeated many times before an appropriate design was found. The cost of the process was enormous. 

Robustness. The program should run for a long time and many molecules before failing, and it should indicate the actions taken on failure rather than simply crash. 

Unanticipated events that occur should be recorded in computer system maintenance records and include what corrective action was taken, who performed the corrective action, and when the action occurred. These events might include system crashes, date/time changes after a power failure, etc. 

The PERT technique was developed in connection with the Navy s crash project to produce the Polaris submarine. It is given much of the credit for the completion of that program 18 months ahead of schedule. In another spectacular success, the turnaround time (the time necessary to shut down, repair, maintain, inspect, and start up the unit) for a methanol unit was cut from 12 to 9 days, with no increase in personnel, by using CPM. This is especially impressive since a similar turnaround had been done annually for 25 years,2 and using the best methods available the turnaround time had never been less than 12 days. 

These generalizations can be applied to any job. There are some activities that cannot be speeded up. Others can be done faster, but in most cases this involves spending more money in obtaining special equipment, hiring more labor, paying overtime, working an extra shift, and so on. For all activities there is some minimum finite performance time. No matter what is done, it cannot be completed any faster. This is called the crush time of the activity, and the cost associated with it is the crush cost. The same is true for projects. The crash cost of a project is the price associated with finishing the project in the crash (minimum) time. 

Figure 13-5 The number of men employed in each activity and totally if the starting times are varied in order to reduce the fluctuations in manpower that occurred in Figure 13-4. The job is still to be completed in the minimum amount of time possible assuming no activities are crashed.

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