Final answer:
The entry permit for a confined space is valid for one year, and employers must do a review of the permit-required confined space program within one year after each entry or a single annual review covering all entries during eighteen months.
Step-by-step explanation:
The entry permit for a confined space is valid for one year. After each entry, employers must review the permit-required confined space program within one year. However, they also have the option to do a single annual review that covers all entries during a specific period. The correct answer to the question is d) Eighteen months.
During the eighteen-month period, the employer must conduct a comprehensive review of the permit-required confined space program, ensuring that all entries comply with the necessary safety regulations. This review helps maintain the safety of workers and prevents any hazardous incidents within confined spaces.