Difference Between CSO/CSE, Key Interlocks and LO/LC

Car seals are single use seals used usually in conjunction with steel cable to keep valve from being opened or closed in error. (Name comes from railroad seals I believe). The only way to defeat them is to cut them open. However, there is also no way to easily check whether the valves have been operated without a physical check in the field.

CSO just means to "car seal open". I think CSE should read CSC - Car seal Closed.

Lock open/lock closed comes in many forms, but this allows a reusable protection system to prevent inadvertent opening or closing of the valve. Each lock has a unique key therefore there is "control" of its use.

Key interlocks are slightly different in that they are usually used on Safety relief systems where you want to make it impossible (very difficult) to block in a relief system. There are two keys involved which are captured by the locks and it is not possible to lock one valve closed without first unlocking and opening the other.

Gives good control and ensures no blocking of a safety relief system.