Title : Explosion in skid mounted Hydrogen compressor panel.
Summary : Vendor supplied high pressure hydrogen compressor ( Positive displacement diaphragm type ) has a panel. As per standard , panel is pressurised by air and has a suction blower fitted at the top. It has all the alarm & trip protections in case of loss of pressurization. Only one multicore instrument signal cable from common junction box on the compressor skid enters the panel. Plant air tubing for pressurization is only other connection.
On 24th Jan 2007 at 02.30 hrs , small explosion took place when operator was stopping the running compressor by pushing STOP push button on panel .Both doors of control panel were thrown out & broke from the hinges. It struck the operator causing minor injury on forehead.
Possible causes :
Hydrogen ingress from plant air going to panel due to back up from valve actuators.
Hydrogen ingress from atmosphere due to loss of pressurization.
Hydrogen ingress through instrument cable.
Actual Cause :
Test by LEL meter established that hydrogen had found entry to panel through the cable.
Root cause :
Diaphragm of pressure switch on compressor suction at 30 Barg had dislocated due to water back up
upset during plant start up 2 days back. Water was only drained , lines blown dry & start up taken.
But hydrogen found its way to instrument junction box as there was fault in instrument cabling.
Secondary cause :
Instrument cables were not with seal as prescribed by standard ISA 12.01.01 - 1999 . This allowed gas
ingress from pressure switch to Jn box & from there through multicore cable to panel.
Systemic root cause :
For major projects , company gives bulk orders for Instrument & Elec.cables & uses them even for
vendor supplied skids. Even though cables are ordered as per applicable specifications , there is a
chance , by mistake wrong specification cable or gland may get used in high hazard zone .
Company should order skids complete with cabling for Zone 1 & 2 areas. This will prevent possible mismatch of specifications during procurement or chance of a wrong cable usage in project stage due to lack of supervision.
In upset conditions such as water back up , company should do ‘ What If ' analysis to judge all possible effects before moving ahead after obvious corrective actions.
Author Contact information :
Name : Shantanu S. Date
Designation : Sr. Vice President
Address : Reliance Industries Ltd , Gr. Mfg.Services, Mumbai, India
Mobile : 0091 9987091801
Office : 0091 22 44779504
Fax :0091 22 44779499
E- Mail : email@example.com