The Chemical Safety Board (CSB) recently released a report about an incident that resulted in two fatalities and numerous injuries in 2013.
An explosion occurred after heat was added to a reboiler on a distillation unit with no access to a pressure relief valve. The exchanger that was believed to be isolated from the process actually contained hydrocarbons either through a leaking valve or valve misalignment. After the heating medium was added to the vessel, the hydrocarbon quickly expanded causing the exchanger to rupture.
One of the primary causal factors I wanted to focus on is providing a route to relief valves on all vessels. In this case, the vessel was taken out of service for maintenance while another exchanger operating in a parallel service was kept in operation. There was one pressure relief valve protecting the shell side of the parallel exchangers and the distillation column in service. Therefore, whenever one exchanger was taken out of service it was isolated from pressure relief.
The following are ideas/steps to implement to prevent this type of incident from occurring:
Verify on Piping and Instrumentation drawings that all vessels have route to relief valve.
Verify Piping and Instrumentation drawings match what is in the field.
In your unit Process Hazard Analysis, consider events that could cause heat medium to be introduced to a process vessel in all modes of operation including when down for maintenance.
Remove valves in between vessels and relief valves. If valves are needed, ensure stringent administrative controls are in place to minimize likelihood of valve misalignment.
When relief valves are taken out of service for maintenance, ensure equipment being protected has a route to an adequately size relief valve.