Devices which limit the worst case, relief scenario

2 DEVICES WHICH LIMIT THE WORST CASE RELIEF SCENARIO 

There are a lot of possible ways in which the worst case relief scenario can be limited. These include  

In all such cases, the adequacy of the relief system depends on the integrity of the method(s) used to limit the worst case. It is important to check regularly that these methods are still in place. 

For mechanical systems (e.g. (a) and (b) above), it is important to ensure that, during maintenance, the safety functions of equipment are recognised. Otherwise, they may be replaced with unsuitable equipment. For instance, it is preferable for flow restrictors to use an orifice welded within a short length of pipe, so that it cannot easily be left out, rather than, an orifice plate that slips between pipe flanges. It is desirable to have some method of clearly indicating that such equipment has a safety critical function. 

The integrity of safety instrumented systems is usually dependent on proof testing at specified intervals (often at a frequency between monthly and three-monthly). Safety management systemst2j need to be in place to ensure this and that any safety critical operating procedures such as described in (c) above are adhered to. 

---