Temporary havens

A temporary haven can be a room or building that, because of its design and construction, can provide protection to a few people for the expected duration of a toxic release. Usually control rooms in plants are set up as safe havens for operators, to enable them to effect an orderly and safe shutdown of the facility and isolate the source of the release. These control rooms are usually fitted out with special HVAC systems that can be shut down quickly, air intakes that close tightly, and a separate supply of breathing air capable of supporting the necessary personnel for an extended period of time. 

Another group of shelters can be classified as temporary havens. They do not provide the same level of protection as a safe haven but can provide shelter at the start of a crisis. A temporary haven is also a room or building that can provide protection from toxic fumes, but for a limited period of time. This may be adequate for toxic gas releases of short duration. However,... 

In emergency response plans, distinction between safe havens and temporary havens should be clear. 

The major reason for considering the use of a safe haven or temporary haven is that immediate evacuation of the people affected may not be feasible. Gardner and Jann (1990) have shown that for chlorine and ammonia leak scenarios where the release duration is ten minutes, indoor sheltering can reduce the risk by 98.5% when compared to outdoor exposure. In this scenario, it was assumed that the building used as the temporary haven had an air change rate of once per hour. 

Procedures and criteria for evacuation versus the use of temporary havens must be developed during the emergency response planning process. Such decisions should not be made casually at the time of the event. 

The mechanism is the most complex you have met and it will help you to recall it if you see it in two halves, each very similar to the other. The reaction starts with a protonation on car-bonyi oxygen and addition of an aicohoi to the C=0 k bond. When you get to the temporary haven of the hemiacetal, you start again with protonation of that same oxygen then lose the OH group by breaking what was the C=0 a bond to form an oxonium ion. Each half goes through an oxonium ion and the aicohoi adds to each oxonium ion. The last step in the formation of both the acetal and the hemiacetal is the loss of a proton from the recently added alcohol. From your complete mechanism you should also be able to verify that acetal formation is indeed catalytic in acid. 

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