The term ‘car seal’ can refer to a device used for locking valves although its origins illustrate that it is still used in others areas of industry today.
The name 'car seal' derives from a device originally used on railway cars to seal the car shut (if it was carrying cargo) and to give evidence of tampering with the contents and these are still used on road going cargo trucks and shipping containers today, especially when they pass through customs.
The concept is identical to a lead seal that is used on an electricity meter to give evidence of tampering.
When it comes to locking valves a car seal is often used as a physical and visual deterrent, warning workers that the valve must not be operated without suitable authority and permit; the consequences of unauthorised valve operation could lead to a hazardous situation. Note therefore that the use has changed from security to safety.
The car seal is a cable with a head on it, usually a small block of aluminum or steel. For locking valves, the cable wraps around the handle or wheel, then around some other part of the valve or adjacent steel/pipe work. The cable is passed into the seal head. A screw with a break-off handle tightens on the cable until it shears off. This is now sealed. (There are other types on the market that don't use a shear of screw).
In valve processes, car seals are used on block valves up and downstream of a safety relief valve (SRV, PSV). To ensure an open path to relief is maintained, the upstream valve is designated CSO – Car Seal Open.
Seals are non-reusable. In order to remove the seal, the cable must be cut. This makes it relatively easy to remove and begin valve operation.
If the consequences of such action must be avoided at all cost, it may be necessary to use a more robust lockout device or even a mechanical valve interlock.
A risk assessment will identify such issues.
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