Physical locks on energy isolating devices is the preferred method for lockout tagout. OSHA 29 CFR 1910.147 does allow tagout only to be used in the following circumstances:
- The energy isolating device cannot be physically locked out.
- The energy isolating device can be locked out, but the employer can demonstrate an equivalent level of protection to physical locks.
When tagout only systems are used, the employer must take additional steps to ensure that this method is as safe as using physical locks. These steps may include removing a valve handle to assure it cannot be turned, or blocking a control switch. When tagout only is used, employees must be trained on the limitations of a tagout only system.
When a tagout device is used on an energy isolating device which is capable of being locked out, the tagout device shall be attached at the same location that the lockout device would have been attached, and the employer shall demonstrate that the tagout program will provide a level of safety equivalent to that obtained by using a lockout program.