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 set of facts and asking how a specific 29 CFR requirement applies, and OSHA's relevant Directorate responds in a signed letter that becomes part of the public record.

OSHA is explicit about what its 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, and it cannot invent a new duty that the standard itself does not contain.

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, and only rulemaking can.

An LOI is official agency guidance and not a regulation. It is not published in the Federal Register and does not go through notice-and-comment rulemaking, and it does not amend the Code of Federal Regulations. Its role is to 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 authority of a letter is more limited. Because an LOI is interpretive guidance rather than a legislative rule, a reviewing court does not treat it as binding law and instead weighs the agency's interpretation under administrative-deference doctrine, considering how thorough, consistent, and persuasive the letter is. An LOI is therefore authoritative but rebuttable, since it tells you where OSHA stands today and shifts the burden onto anyone arguing that the agency is wrong.

OSHA states one more limit 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 is on osha.gov under the path /laws-regs/standardinterpretations, and the index can be filtered 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 with the pattern 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.

First, identify the exact 29 CFR provision your question turns on. Second, filter the interpretations index by that standard number, which returns every letter OSHA has issued on that provision, newest first. Third, 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, since 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 its date, its addressee (the person or organization OSHA wrote back to), and the 29 CFR provision it interprets. A suitable form is OSHA Standard Interpretation, "[short subject]," to [recipient] (Month Day, Year), interpreting 29 CFR [section], followed by a link to the osha.gov page so a reader can open the source.

When you build a written compliance position, such as 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, and then state your conclusion. OSHA reasons in the same order, with the statute and standard first and the 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 commentary on a regulation, and a single sentence quoted out of context can read more broadly than OSHA intended, so state the rule first, then the letter, then why the two agree.

When the published letters do not answer your situation, 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, which are 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 affects the quality and speed of the answer, because a structured request with background, question, and position with citations gives reviewers less to decode and reduces follow-up correspondence.

Cairn's LOI Drafter can prepare the request. It turns a compliance chat into a structured request with the background, question, and position and the citations already attached, and it exports a print-ready PDF on your letterhead that mirrors OSHA's own letter format.