What is an OSHA Letter of Interpretation? (And how to use one.)

A Letter of Interpretation (LOI), which OSHA calls a "standard interpretation," is the agency’s written answer to a question about how one of its standards applies to a particular situation. Someone (often an employer, a safety professional, or a trade association) writes to OSHA describing a fact pattern and asking how a specific 29 CFR requirement applies; OSHA’s relevant Directorate responds in a signed letter that becomes part of the public record.

OSHA is explicit about what these letters are and are not. On its interpretations index, the agency writes: "OSHA requirements are set by statute, standards, and regulations. Our interpretation letters explain these requirements and how they apply to particular circumstances, but they cannot create additional employer obligations." In other words, an LOI tells you what an existing rule already means for your facts. It cannot invent a new duty that the standard itself does not contain.

That distinction matters in practice. If an LOI says a given guardrail configuration satisfies 29 CFR 1926.501(b)(13), you can rely on it as OSHA’s stated position. If you wish OSHA had a rule it does not have, no letter can create one; only rulemaking can.

An LOI is official agency guidance, not a regulation. It is not published in the Federal Register, it does not go through notice-and-comment rulemaking, and it does not amend the Code of Federal Regulations. What it does is tell you, and OSHA’s own compliance officers, how the agency reads a standard it already enforces.

For day-to-day compliance, an on-point letter is strong evidence that you read the standard the way the agency does, and OSHA compliance officers are expected to apply the agency’s published interpretations consistently. Citing the controlling LOI in a written position can resolve a question before it becomes a citation.

In litigation the weight is more nuanced. Because an LOI is interpretive guidance rather than a legislative rule, a reviewing court does not treat it as binding law; it weighs the agency’s interpretation under administrative-deference doctrine, considering how thorough, consistent, and persuasive the letter is. So an LOI is best understood as authoritative but rebuttable: it tells you where OSHA stands today, and it shifts the burden onto anyone arguing the agency is wrong.

One more limit OSHA states directly: "These letters of interpretation and the standards they address may not apply to OSHA State Plans. State Plans are required to have standards and enforcement programs that are at least as effective as OSHA’s and may have different or additional requirements." If you operate in a State Plan state (for example California, Washington, or Michigan), confirm the state’s own position before relying on a federal letter.

Every published letter lives on osha.gov under the path /laws-regs/standardinterpretations. The index is filterable by keyword, by standard number (for example "1910.147"), and by year, with letters dating back to 2000. Individual letters use a date-based URL, the pattern is osha.gov/laws-regs/standardinterpretations/[date], and each page shows the original inquiry, OSHA’s response, the signing official, and the standards the letter addresses.

A reliable workflow: identify the exact 29 CFR provision your question turns on, then filter the interpretations index by that standard number. The result is every letter OSHA has issued touching that provision, newest first. Read the most recent on-point letter first, because a later letter can refine or supersede an earlier one.

Always pair the letter with the live regulation. Read the controlling standard text on osha.gov/laws-regs or the official eCFR at ecfr.gov, because an interpretation can be overtaken by a later rule change. OSHA says as much: its "enforcement guidance may be affected by changes to OSHA rules," and the agency updates guidance "in response to new information." A letter from 2003 interpreting a standard that was amended in 2016 may no longer reflect current law.

Cite an LOI by three things: the date, the addressee (the person or organization OSHA wrote back to), and the 29 CFR provision it interprets. A clean form is: OSHA Standard Interpretation, "[short subject]," to [recipient] (Month Day, Year), interpreting 29 CFR [section]. Then link the osha.gov page so a reader can open the source.

When you build a written compliance position, say, a response to a citation, an internal program justification, or your own request for a new interpretation, lead with the controlling standard text quoted from 29 CFR, then cite the LOI that supports your reading, then state your conclusion. That ordering mirrors how OSHA itself reasons: statute and standard first, interpretation second.

Never cite a letter you have not read in full, and never cite one without also citing the underlying standard. An LOI is a gloss on a regulation; quoted out of context, a single sentence can read more broadly than OSHA intended. State the rule, then the letter, then why the two agree.

When the published letters do not answer your fact pattern, you can ask OSHA for a new one. Submit a written request to the OSHA Directorate responsible for the standard at issue. A well-formed request has three parts: the background (the specific facts and operations involved), the precise question you want answered, and your own position with citations to the relevant 29 CFR provisions.

OSHA does not publish a fixed turnaround, and complex questions can take several months. The quality of your request drives the quality and speed of the answer: a structured request, background, question, and position with citations, gives reviewers less to decode and reduces follow-up correspondence.

Cairn’s LOI Drafter does this work for you. It turns a compliance chat into a structured request, background, question, and position with the citations already attached, and exports a print-ready PDF on your letterhead that mirrors OSHA’s own letter format.