29 CFR 1960.28(d) provides instructions for Employee Reporting of Unsafe or Unhealthful Working Conditions:

Reports received by the agency.

1960.28(d)(1)
Each report of an existing or potential unsafe or unhealthful working condition should be recorded on a log maintained at the establishment. If an agency finds it inappropriate to maintain a log of written reports at the establishment level, it may avail itself of procedures set forth in 1960.71. A copy of each report received shall be sent to the appropriate establishment safety and health committee.

1960.28(d)(2)
A sequentially numbered case file, coded for identification, should be assigned for purposes of maintaining an accurate record of the report and the response thereto, As a minimum, each establishment's log should contain the following information: date, time, code/reference/file number, location of condition, brief description of the condition, classification (imminent danger, serious or other), and date and nature of action taken.