29 CFR 1910.119(d)(3)(i)(D) requires process safety information on relief system design and design basis, and (d)(3)(i)(F) requires the design codes and standards employed. Relief devices are also mechanical integrity equipment under (j)(1)(iii). OSHA's letters on relief systems are few, but they make clear that the design basis has to be documented with its assumptions and calculations, and that alternatives to relief devices are judged against recognized engineering practice.

What OSHA Has Said

Dec 22, 2003
Design basis documentation must include codes, assumptions, and calculations
A pipeline company asked how to document the design basis for building ventilation under (d)(3)(i)(E). OSHA said the PSI must include the design basis, the codes and standards employed under (d)(3)(i)(F), and all assumptions and calculations. Industry standards such as NFPA 30, NFPA 58, and IIAR Bulletin 111 can serve as the design basis. OSHA also pointed out that API 500 does not allow ventilation to reclassify an enclosed area handling hydrocarbons as unclassified, so documentation claiming that would violate (d)(3)(ii). A company's own standard qualifies only if it reflects recognized and generally accepted good engineering practice.
Read OSHA Letter ↗
Jun 4, 2018
Relief for positive displacement pumps, and SIS as an alternative
In a letter on positive displacement pumps, OSHA addressed an employer that used a safety instrumented system designed to ISA 84 in place of pump relief protection, and said the deviation would be treated as de minimis. The same letter said the atmospheric storage exception does not apply to tanks connected to the process. Read the letter for the conditions OSHA attached.
Read OSHA Letter ↗
Mar 5, 1998
Equipment built to older code editions
An engineering firm asked about vessels built to the 1972 edition of ASME Section VIII. OSHA said an older edition counts as a code "no longer in general use" under (d)(3)(iii). The employer must determine and document that the equipment is designed, maintained, inspected, tested, and operated safely, and that determination becomes the baseline for future inspection and maintenance. Recalculation isn't required where the original design is consistent with current editions, but differences must be documented and justified. Where no records exist for materials, welding, or radiography, it is appropriate to assume the lowest values in the engineering analysis.
Read OSHA Letter ↗
Feb 4, 2013
Relief devices are mechanical integrity equipment
OSHA confirmed that pressure relief devices fall under mechanical integrity at (j)(1)(iii), and that employees who maintain them are trained under (j)(3): an overview of the process and its hazards plus the procedures for their tasks. Employers choose how to deliver that training rather than being bound to manufacturer courses.
Read OSHA Letter ↗

⚡ Key Compliance Takeaway

For every relief device, you should be able to produce the governing scenario, the required relief rate, the sizing calculation, and the code used. When records are missing, rebuild them with conservative assumptions. If you rely on an instrumented system instead of relief, document the design to a recognized standard such as ISA 84 and why it protects against the relief scenario. Then keep the devices in your inspection and testing program.