To anyone responsible for safety at a hydrocarbon storage and transfer facility, the names Buncefield and Caribbean Petroleum Bayamón will likely conjure up thoughts of catastrophic explosions and fires resulting from overfilling incidents. Analysis of these and similar disasters suggest such incidents are the result of failures, or the absence, of four systems:
- The plant’s basic process control system (BPCS), leaving operators with a false indication of the fullness of a given tank.
- Overfill protection mechanisms, which should automatically shut down a transfer when nearing capacity, but instead allow liquid fuels to escape.
- Gas detectors, which should call attention to flammable vapour clouds forming from a spill in progress.
Fire detectors, which should trigger suppression systems and alert operators when a fire breaks out.
These systems represent sequential layers of protection for the facility, moving from prevention to mitigation, each offering an ability to stem an incident before it moves to the next level of damage.
This article will take a brief look at all four of these systems individually in the context of fixed and floating roof tanks to understand how they can be improved and optimised to deliver their protective function.Understanding overfill prevention
The most effective way to avoid an incident is to keep flammable liquids inside the tanks. The most common source of releases, outside of a pipe or valve failure, is overfilling, as was the case in the incidents previously mentioned. Such incidents happen when operators do not have an accurate indication of a tank’s contents and end up forcing in more liquid than it can hold. This stems from ineffective level instrumentation, resulting in poor situational awareness for the operators: the tank they are trying to fill is already fuller than they realise. This should be stopped by an automatic safety system that is able to shut down a liquid transfer, or at least trigger an alarm to warn operators of the developing situation…
Written by Joshua Hernandez and Helena Hjortsberg, Emerson.
This article was originally published in the Summer 2020 issue of Tanks & Terminals. To read the full article, and other great technical articles in this issue, view the full issue here. You can also register to receive a free regular copy of the magazine here.
Read the article online at: https://www.hydrocarbonengineering.com/special-reports/03062020/a-coordinated-strategy/