The lock is the key part of any lockout-tagout program, and when it is used properly and meets all of OSHA’s physical requirements for a lockout lock, then it will keep employees safe."
To protect the integrity of the lock and the lockout program all lockout locks must be standardized at each facility so that when seen by any employee the employee will know its purpose, and not attempt to bypass the lock.
A Guide to Selecting and Standardizing
OSHA has strict requirements set in place restricting which locks can be used as lockout locks. The purpose of these physical requirements is to first and foremost protect the employees through the physical protection of a lock, and to protect the integrity of the lockout program. The lockout lock physical requirements, as OSHA 1910.147 states, are that lockout devices shall be durable, standardized, identifiable, and not used for other purposes.
The main purpose of applying a lock to an isolation point for each energy source is to provide physical protection against anyone reenergizing the equipment being serviced. In order to provide this protection the lock must be able to withstand the environment it is exposed to without wearing or corroding before it is removed. The lock must also be strong enough to prevent its removal without the use of excessive force or a lock removing tool.
To protect the integrity of the lock and the lockout program all lockout locks must be standardized at each facility so that when seen by any employee the employee will know its purpose, and not attempt to bypass the lock. Locks must be standardized by at least one of the following characteristics:


Color
Shape
Size


The industry standard is to use all red locks to avoid confusion, but if desired to identify locks by department it is also acceptable for example to use all 2 inch square locks, or different sized circular locks and assign each department its own color.
Each lock must identify the person who applied the lock. This can be done with locks that have a space for the owner to write