Here is the section of the OSHA General Industry stds covering how/who/when to take off a lock or tag. It is the responsibility of your employer to have a written policy or program that describes what should happen and who should be contacted (not just by voice mail or email) before an attempt is made to remove the device of an employee who is not available to remove it him/herself. (In parts 1910.147(e)(3)(i), (ii) & (iii), the term authorized employee means the employee who originally installed the lock or tag.) I have seen employers who use logbooks, etc.
Your employer's documented procedure should include a section on what to do if a supervisor or company rep is not available. (My bolds.)
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1910.147(e)(3): Lockout or tagout devices removal. Each lockout or tagout device shall be removed from each energy isolating device by the employee who applied the device.
Exception to paragraph (e)(3): When the authorized employee who applied the lockout or tagout device is not available to remove it, that device may be removed under the direction of the employer, provided that specific procedures and training for such removal have been developed, documented and incorporated into the employer's energy control program. The employer shall demonstrate that the specific procedure provides equivalent safety to the removal of the device by the authorized employee who applied it. The specific procedure shall include at least the following elements:
1910.147(e)(3)(i)
Verification by the employer that the authorized employee who applied the device is not at the facility:
1910.147(e)(3)(ii)
Making all reasonable efforts to contact the authorized employee to inform him/her that his/her lockout or tagout device has been removed; and
1910.147(e)(3)(iii)
Ensuring that the authorized employee has this knowledge before he/she resumes work at that facility