What happened
On 22 October 2009 gasoline overflowed from a storage tank at the Caribbean Petroleum (CAPECO) terminal near San Juan, Puerto Rico. The spray formed a large vapour cloud that ignited. The U.S. Chemical Safety Board found that the facility relied on a float-and-tape level system as its only overfill control, that the tank's electronic level transmitter was out of service so operators recorded levels by hand, and that the measuring devices were poorly maintained. There was no independent high level alarm and no automatic overfill prevention. There were no fatalities, but around 300 nearby homes and businesses were damaged.
The CSB recommended regulations requiring automatic overfill protection, regular testing and risk assessment for flammable storage tanks.
Lessons for SIS and instrumentation
- A single layer is not enough for a catastrophic scenario. Overfill of flammable liquid needs layers independent of the basic gauging.
- Manual monitoring is a weak substitute when the transmitter is out of service; define compensating measures and limits on operation without the instrument.
- Maintenance of level instruments is safety work and needs the same discipline as SIS maintenance.
Related First Out AI articles
"Lessons from Buncefield (2005)", "HAZOP deviation library: atmospheric storage tanks", "Managing bypasses, overrides and start-up inhibits".
Written for First Out AI as engineering guidance. It supports engineering work and does not replace it; check every value against your standards, certificates and company rules with a competent functional safety engineer.