Design Out the Hazard

NASA has developed an extremely useful hierarchy of hazard reduction (National Aeronautics and Space Administration, 1993). This method is applicable to all industries. The first step is to design out the hazard. If this is not possible, then the next best is to use safety devices. If safety devices are not sufficient control, then cautions and warnings can be applied. And finally, special procedures and training can be used to control the hazard or mitigate the consequences. 

System Safety Engineering and Risk Assessment A Practical Approach 

In the late 1980s, NASA experienced such a problem (National Aeronautics and Space Administration, 1989). After arrival at the Kennedy Space Center for Space Shuttle launch preparations, the Magellan spacecraft power control unit was reconnected. An extensive electrical power system check was necessary to ensure proper performance prior to applying power to other spacecraft subsystems. A technician was making a blind mate (mating cables without visual verification during the operation) of an electrical harness power cable to the Magellan. Because the connection was buried deep in the spacecraft, out of view of the technician, it was impossible to verify visually that the connection was correct. Sparks, flames, and smoke resulted from the cable connection operation. 

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This chapter identifies the factors which determine whether a guard or safety device taken together with appropriate systems of work, supervision, instruction, maintenance, and permit-to-work procedures are adequate. In practice the most effective method of preventing machinery accidents, apart from designing out the hazard, is to minimise the need for access, whether operationally-required or unofficially desirable. The effort which has to be devoted to the design of ingenious safety devices, the development of complex systems of work, and the provision of close supervision, is largely a... 

The facility hazard analysis follows the same path and sequence of order as the hazard analysis process (review Figure 5.2 to refresh your memory). As mentioned in Section 2.6, the safety managanent system in a facility should also use the hazard reduction precedence design out the hazard, use safety devices, use warning devices, and finally, use special procedures and training. 

In reviewing the hazard analysis worksheets, you can see that gas detection is important. The experiment is flying in a closed-in environmenL so laser gas leakage is a very real concern. Many times engineers forget to add appropriate monitoring systems. Of course, designing out the hazard would have been the best solution if it were possible. 

If you add cost data with each hazard control and then trend the success of those data, you are well on your way to modeling the cost of upgrading the system. You can take the entire hazard analysis process and change out the hazards for design or operational trade-off ideas, associate costs to each trade-off, trend the data with any typical statistical package, and have a pretty elaborate efficiency and productivity analysis of your system. 

An electrician went up a ladder to repair a light fitting and was affected by fumes coming out of a vent about a meter away. The electrical hazards and the hazards of working from a ladder were considered, but no one thought about the hazards introduced by the vent—yet vents are designed to vent. 

Many of the incidents in this book were the result of leaks of hazardous materials, and the recommendations describe ways of preventing leaks by providing better equipment or procedures. As we have seen, equipment can fail or can be neglected, and procedures can lapse. The most effective methods, therefore, of preventing leaks of hazardous materials are to use so little that it hardly matters if it all leaks out (intensification or minimization) or to use a safer material instead (substitution). If we cannot do this and have to store or handle large amounts of hazardous material, we should store or handle it in the least hazardous form (attenuation or moderation). Plants in which this is done are said to be inherently safer because they are not dependent on added-on equipment or procedures that might fail the hazard is avoided rather than controlled, and the safety is inherent in the design. 

Adequate engineering design for the duty intended Hazard studies ( What if ) carried out ... 

After obtaining the prototypes, tests must be made to determine the utility. Generally these include a short time destructive test to determine the strength and to check out the basic design. Another test that is done is to use the product in the projected environment with stress levels increased in a rational manner to make for an accelerated life test. Other tests may include consumer acceptance tests to determine what instructions in proper use are required, tests for potential safety hazards, electrical tests, self-extinguishing tests, and any others that the product requires. In the case of high risk products, the test program is continued even after the product enters service. 

Table 13.16 sets out the major waste disposal methods, and potential hazards from toxic waste deposition are indicated in Table 13.17. The range of precautions required at land tips depends upon the risk, e.g. the nature and degree of contamination and the work to be undertaken. It will, however, encompass personal protective equipment a high standard of personal hygiene enclosure, possibly pressurization, and regular cleaning of vehicle cabs vehicle washing facilities site security, and control of designated dirty areas. Air monitoring and medical surveillance may be required.

As the flowsheet becomes more firmly defined, the detailed process and mechanical design of the equipment can progress. The control scheme must be added and detailed hazard and operability studies carried out. All this is beyond the scope of the present text. However, all these considerations might require the flowsheet to be readdressed if problems are uncovered. 

Reactions of boron hydrides must be carried out with special care. If properly conducted, the reactions reported here proceed without difficulty, but fires which do occur as the result of equipment failures or similar incidents are usually vigorous. It is recommended that all carborane preparations be carried out in areas designated for the use of hazardous materials. 

In the Mond Index the plant is divided into individual units on the basis of the feasibility of creating separating barriers. One of the factors taken into account in the index is therefore plant layout. The potential hazard is expressed in terms of the initial value of a set of indices for fire, explosion and toxicity. A hazard factor review is then carried out to see if design changes reduce the hazard, and intermediate values of the indices are determined. Offsetting factors for preventative and protective features are applied and the final values of the indices, or offset indices, are calculated. The elements of the Mond method are listed in Table 1. 

The inherent safety is the pursuit of designing hazards out of a process, as opposed to using engineering or procedural controls to mitigate risk. Therefore inherent safety strives to avoid and remove hazards rather than to control them by added-on systems. The inherent safety is best considered in the initial stages of design, when the choice of process route and concept is made. 

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