Time to evacuate

To estimate the time required for an ejector to evacuate a system from atmospheric pressure down to the design pressure, assume that the average air handling capacity during the evacuation period is twice the design 

If this approximate evacuation period is too long, it may be shortened by adding a larger last stage to the ejector or by adding a noncondensing ejector in parallel 

Equipment Design Handbook for Refineries and Chemical Plants, Vol. 1, 2nd Ed.. Gulf Publishing Co., 1979. 

one must estimate air or other gas leakage into the vacuum system. Of course every effort is made to keep it as tight as possible. The author is aware of possible leak points being sealed with polystyrene, which produces an excellent seal. When tests cannot be made, one must use rules of thumb. Many such rough estimating techniques exist. 

Te = Time to evaeuate a system from atmospheric pressure to the design pressure of an injector, min. 

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Elame-spread and smoke-density values, and the less often reported fuel-contributed semiquantitive results of the ASTM E84 test and the limited oxygen index (LOI) laboratory test, are more often used to compare fire performance of ceUular plastics. AH building codes requite that ceUular plastics be protected by inner or outer sheathings or be housed in systems aH with a specified minimum total fire resistance. Absolute incombustibHity cannot be attained in practice and often is not requited. The system approach to protecting the more combustible materials affords adequate safety in the buildings by aHowing the occupant sufficient time to evacuate before combustion of the protected ceUular plastic. 

It is common in many offshore areas to encounter a shallow gas hazard. Quite often, these hazards can be spotted on seismic, and a surface location is chosen to avoid the hazard. However, there is always a risk of encountering a shallow gas flow with insufficient casing in the well to allow a shut-in. In this instance a diverter system is called on as a safety measure. The ideal function of the diverter system is to allow the well to flow and subside by natural means. In many cases the diverter system simply provides enough time to evacuate the rig. 

True. Smoke alarms will sound long before the levels of smoke become dangerously high. This provides people with valuable time to evacuate a burning... 

The API 521 also recommends locating ladders and platforms on towers and elevated structures on a side away from the flare. Designing in this manner provides personnel a shield from the radiant heat allowing them more time to evacuate the area. 

In a major collision accident, is there adequate warning time to evacuate people to a safe location ... 

Sometimes in the case of a chemical spill a decision must be made whether to evacuate the public or to have people remain inside buildings with windows closed until the toxic cloud has passed. If there is time to evacuate, this is usually the choice that is made. Evacuation may be ordered if no spill has actually occurred but there is potential for a release, as in a transportation accident or fire. But sometimes the toxic cloud forms quickly or there may be a wind shift so that there is no time to evacuate. Responders may also recommend that people remain indoors with windows closed in fringe areas, such as (1) in areas not directly downwind or (2) when the toxic cloud has become diluted to the point where outdoor concentrations are below ERPG-2 levels, or (3) when the toxic cloud passage is very brief If it is practical to evacuate, this is the preferred choice. 

Research has shown that Phase 1 can be as long as two-thirds of the total evacuation time required. The most important variable to consider when assessing means of escape provision is the construction of the building. If the building is less likely to burn or allow rapid fire spread the occupants will have more time to evacuate and therefore a better chance of escape. (Chapter 10 explores reasons why people may delay reacting to a fire alarm.)... 

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