Extra security
January 1st 2006

Trapped key interlocks from Castell are helping to protect maintenance workers at the UK's first under ground liquid hydrogen bus refuelling station near Hornchurch.

To combat any fire risk, the site's three-level, 55 000L storage vessel is protected by a CO2 deluge system. BOC, the company responsible for the project on behalf of BP - wanted a mechanical safeguard to ensure nobody could gain access to the chamber while the CO2 supply was active.

Now, when entry to the chamber is required, a 3-way MBV ball valve interlock must first be set to discharge to atmosphere. The interlock releases a coded key that is inserted into the lock fitted to the chamber door, allowing the door to be opened. The key is trapped in the lock, while a second key is released. By retaining this key, any worker entering the chamber ensures that the CO2 supply cannot be re-established.

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