PRESSURE RELIEF VENTING SYSTEMS - EXAMPLES OF GOOD AND BAD PRACTICE

Pressure relief systems employed at chemical and petrochemical sites are a key safety measure. It is important that they are sized correctly so that they would function effectively if needed. The venting systems protect process vessels against various relief cases including fire and runaway chemical reactions. Through its role in providing technical support to Health and Safety Executive (HSE) inspectors, the Health and Safety Laboratory (HSL) is well placed to be aware of current industry practice and problems in pressure relief vent sizing. Although there is considerable guidance on good vent design, some misunderstandings and errors are still made, thus the key knowledge required and guidance sources needs to be reinforced. Examples of both good and bad practice are described. Bad practices include: runaway reactions cases not considered and vent lines and catch tanks made from unsuitable materials or not pressure resistant. Guidance on the design of venting systems are also discussed, including relevant API pressure relief codes, ISO standards on safety valves and bursting discs and HSE guidance on chemical reactor vent sizing.