Protective measures venting

Testing should address the maximum operating temperature and pressure normally seen at the arrester location. This does not include certain pressure upsets (such as emergency shutdown) that produce unusually high system pressures. In many cases it may not be possible to design an arrester that will function effectively during upset conditions, and other protective measures should be considered (e.g., venting, suppression). 

Example 1—Protective Measures for a Vent Manifold System... 

FIGURE 9-1. Vent manifold system protective measures. 

Since most storage tanks release flammable vapors at seals and vents, they are susceptible to lightning induced fires. Common European practice is to provide lightning rods on the highest vessel at a facility to provide a cone of protection for the facility. NFPA 780 provides additional guidance for the provisions of lightning protection measures. 

Explosion protection measures expect the explosion to take its course, but ensure that it does so safely without any effects on the personnel and equipment. The three possible ways of protection from a hre or explosion are (1) venting (2) containing and (3) suppressing. 

In the event of an alarm, an automatic sequence of actions should make the plant safe without the intervention of an operator. The sequence is likely to be simplest for continuous or semi-batch processes typically it may involve no more than stopping the reactant feeds, provided there are no problems with accumulation of reactants. Batch reactors are more difficult, particularly if they contain large amounts of unreacted material and are more likely to require the provision of protective measures such as emergency relief venting, or the provision of dump tanks with drown out facilities. 

It should also be ensured that the construction of extensions does not in any way compromise the effectiveness of existing gas protection measures (e.g. by blocking vents to the underfloor void or damaging existing membranes). 

All gas protection measures require maintenance. Even passive systems require regular inspections to ensure that vents are not blocked and are still working. The importance of maintenance is highlighted by the example in Chapter 1 where a vent trench became blocked, thus causing an explosion in a building. 

Comparison of E] q)losion Protection Design Measures In Table 26-24, comparison is made of the explosion protection design measures of containment, explosion venting, and explosion suppression. Regarding the effectiveness of the different explosion design measures, all three techniques are equal if the design of these measures is performed properly. 

Table 7-31 lists the explosibility index that is a relative measure of the potential damage from a dust explosion. A rating of 2 to 4 requires large vent areas. Above 4, for most cases, the explosion cannot be controlled by venting design and therefore requires the use of protection such as inert gas or explosive suppression systems, some of which are commercially available. 

In some powder handling processes it is not possible to avoid the simultaneous presence of an explosible dust cloud and a hazardous buildup of charge. In those situations, measures should be taken to protect against or prevent explosions. These include inerting, use of explosion-resistant equipment, explosion venting, or explosion suppression. 

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