ISO 17712 defines a seal as a device with a unique identifier, usually single-use and fitted to the outside of the doors; as part of a security system, its purpose is to show whether unauthorised entry has taken place. A lock, by contrast, tries to delay entry.
Seals fall into three classes by strength: a high-security seal needs heavy bolt or cable cutters, a security seal yields to lightweight tools, and an indicative seal can be broken by hand or with a simple snip. An indicative seal therefore stops nothing and only leaves evidence.
A seal's evidence value comes from its record:
- Write the number on the dispatch document and photograph the fitted seal.
- At delivery, compare the number and condition with the document.
- Put a broken, different or unreadable seal on a report and tell the person responsible.
If a lock is needed, the container must have a point designed for it; a hole drilled afterwards breaks the insulation and weakens the shell. For a seal, the latch hole on most containers is enough.
On a valuable load the lock makes access harder while the numbered seal and the temperature record tell what happened on the road. A seal only works when it is recorded: under ISO 17712, selecting, storing, accounting for and fitting it are part of the system.
