1,3-Butadiene scope and application

This 1,3-Butadiene standard applies to all occupational exposures to 1,3‑Butadiene (BD) unless a specific exemption in paragraph (a)(2) applies. Employers must treat workplace activities involving BD as covered by 1910.1051(a)(1) unless they meet one of the limited exceptions in 1910.1051(a)(2).

• See the full scope at 1910.1051(a).

An employer may rely on objective data instead of performing exposure monitoring when that data reasonably demonstrates the product, stream, or operation will not release BD at or above the action level or STEL under the conditions that could cause the greatest release. See 1910.1051(a)(2)(i).

• "Objective data" can include prior monitoring, validated modeling, or calculations based on the material's composition and properties (see the definition of objective data in 1910.1051(b)).
• If relying on objective data, the employer must keep the data and the basis for relying on it in accordance with recordkeeping rules (see 1910.1051(a)(3) and 1910.1051(m)(1)).

Yes—work operations where the only BD exposure is from liquid mixtures containing 0.1% or less BD by volume (or vapors from those liquids) are excluded from most requirements of the standard unless objective data show such mixtures can generate airborne concentrations at or above the action level or STEL under predictable conditions. See 1910.1051(a)(2)(ii).

• Even when exempt under this paragraph, if objective data later show exposures can exceed the action level or STEL, the employer must comply with the standard and retain the records supporting the exemption per 1910.1051(a)(3).

Yes—except for labeling and emergency response requirements, storage, transportation, distribution, or sale of BD or BD-containing liquids in intact containers or sealed transportation pipelines that fully contain BD vapors are not covered by most provisions of this standard. See 1910.1051(a)(2)(iii).

• Labeling and emergency response rules still apply even when containers are intact.
• Note: other OSHA standards (for example, Process Safety Management) could still apply depending on quantities and on-site activities; you should evaluate other standards that may cover storage or aggregation of hazardous chemicals.

When an employer claims an exemption under paragraph (a)(2) based on objective data, the employer must retain the objective data and the basis for relying on that data as required by the recordkeeping rule in [1910.1051(m)(1)]. See 1910.1051(a)(3) and 1910.1051(m)(1).

• Keep clear documentation showing what objective data were used, how they apply to your product or operation, and why they demonstrate exposures will not reach the action level or STEL under the worst‑case predictable conditions.

The action level for 1,3‑Butadiene is 0.5 ppm averaged over an 8‑hour period. See the definition of action level in 1910.1051(b).

• Reaching or exceeding the action level triggers required monitoring and certain preventive steps under the standard (see monitoring rules at 1910.1051(d)).

The employer must ensure no employee is exposed above 1 ppm as an 8‑hour TWA and no employee is exposed above 5 ppm over any 15‑minute sampling period (STEL). See 1910.1051(c)(1) and 1910.1051(c)(2).

• Manage controls and work practices to keep exposures below both limits.

Employee exposure determinations must be made from breathing‑zone air samples that represent each employee's 8‑hour TWA and 15‑minute short‑term exposures. See 1910.1051(d)(1)(i).

• Use personal breathing‑zone sampling rather than distant area samples when you need to know an individual's exposure.

Representative 8‑hour TWA exposure is based on one or more full‑shift samples for each shift and for each job classification in each work area; representative 15‑minute short‑term exposures require one or more samples tied to operations most likely to exceed the STEL for each shift and job class. See 1910.1051(d)(1)(ii) and 1910.1051(d)(1)(iii).

• If exposures are equivalent across shifts, you may sample only the shift expected to have the highest exposure except for initial monitoring (see 1910.1051(d)(1)(iv)).

Initial monitoring must be completed within 60 days after BD is introduced into the workplace unless the employer relies on acceptable objective data under [1910.1051(a)(2)(i)]. See 1910.1051(d)(2)(i).

• If you have valid objective data that meets the criteria in 1910.1051(a)(2)(i), you may use it instead of performing initial monitoring.

Yes—monitoring done within two years before the effective date can be used to satisfy initial monitoring if it meets all requirements of the standard and workplace conditions have not changed in ways that could cause new or additional exposures. See 1910.1051(d)(2)(ii).

• Verify that the earlier monitoring covered the same operations, job classifications, shifts, and worst‑case conditions as required by the standard.

Monitoring frequency depends on initial results: if initial monitoring shows exposures at or above the action level but at or below the PEL and STEL, repeat monitoring every 12 months; if above the 8‑hour TWA limit, repeat at least quarterly until two samples per quarter are collected over two years, then every six months; if above the STEL, repeat short‑term monitoring at least quarterly with the same two‑samples‑per‑quarter rule before switching to six‑month frequency. See 1910.1051(d)(3)(i)–(iii).

• Follow the schedule appropriate to the level of overexposure your initial monitoring identifies.

An employer may change required representative monitoring from every six months to annually if two consecutive measurements, taken at least 7 days apart, show employee exposure decreased to or below the 8‑hour TWA limit but remains at or above the action level. See 1910.1051(d)(3)(iv).

• Ensure the two measurements meet the timing and representativeness requirements before reducing frequency.

You may discontinue monitoring if initial monitoring shows exposures below the action level and at or below the STEL; likewise, periodic monitoring can be discontinued for employees represented by monitoring if two consecutive measurements at least 7 days apart show exposures below the action level and at or below the STEL. See 1910.1051(d)(4)(i)–(ii).

• Keep records of the measurements used to justify discontinuing monitoring.

Employers must institute additional monitoring whenever changes in production, processes, controls, personnel, or work practices may result in new or additional exposures, or whenever spills, leaks, ruptures or breakdowns may have caused exposures above the 8‑hr TWA or STEL. After cleanup or repair, monitor (using appropriate methods) to ensure exposures returned to pre-incident levels. See 1910.1051(d)(5)(i)–(ii).

• Typical triggers include engineering changes, new equipment, and incidents involving releases.

Monitoring must be accurate at a 95% confidence level to within ±25% for airborne concentrations at or above the 1 ppm TWA limit, and within ±35% for concentrations at or above the action level (0.5 ppm) but below 1 ppm. See 1910.1051(d)(6).

• Use validated sampling and analytical methods that meet these accuracy criteria when assessing compliance.

The employer must notify each affected employee of monitoring results within 15 working days after receiving the results, either individually in writing or by posting results in an accessible location; if the results indicate the 8‑hour TWA or STEL has been exceeded, the employer must, within 15 business days, provide affected employees written information about corrective actions and the schedule for completion. See 1910.1051(d)(7)(i)–(ii).

• Keep records showing when and how notifications and corrective action notices were provided.

A regulated area must be established where airborne concentrations of BD exceed or can reasonably be expected to exceed the 8‑hour TWA limit of 1 ppm or the STEL of 5 ppm for 15 minutes. See the regulated area definition in 1910.1051(b).

• Limit access to authorized persons and use required controls and PPE inside regulated areas.

Objective data includes monitoring data, mathematical modeling, or calculations based on the composition and chemical/physical properties of a material, stream, or product that reasonably demonstrate exposures will not reach the action level or STEL under the worst predictable conditions. See the definition in 1910.1051(b) and the allowance to rely on such data in 1910.1051(a)(2)(i).

• Maintain documentation showing how the data were generated and why they apply to your operation per 1910.1051(m)(1).

Yes—while 1910.1051(a)(2)(iii) excludes intact‑container storage from most requirements of the BD standard (except labeling and emergency response), other OSHA standards—such as Process Safety Management (PSM)—may still apply depending on the quantity and onsite activities. OSHA has advised that storage of pre‑charged equipment or aggregated flammable gases on site in one location can meet PSM coverage criteria. See OSHA's PSM interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06 for further guidance on aggregation and storage under PSM.

• Evaluate your facility for coverage under other standards even when BD is in intact containers; documentation and hazards analysis should reflect any overlapping requirements.

Yes — affected employees or their designated representatives must be given an opportunity to observe any monitoring of employee exposure to BD. Employers are required to provide this opportunity under 1910.1051(d)(8)(i), so you should set up procedures that let employees or their reps watch monitoring activities.

The employer must provide the observer with the required protective clothing and equipment at no cost and ensure the observer uses it and follows safety procedures. This is specified in 1910.1051(d)(8)(ii). Employers should also train observers in use of the equipment and any site-specific procedures before allowing entry.

An employer must establish a regulated area whenever BD airborne concentrations exceed or can reasonably be expected to exceed the 8‑hour TWA or the STEL, limit access to authorized persons, and demarcate the area to minimize the number of employees exposed. This requirement is in 1910.1051(e)(1)–(3). Practical steps include signage, physical barriers, and written access rules communicated to affected personnel.

The host employer must communicate the regulated area's access restrictions and locations to other employers with operations at the worksite whose employees may need access. This communication duty is stated in 1910.1051(e)(4). The communication should be clear, in writing when appropriate, and include how to request authorization and required protective measures.

The employer must institute feasible engineering controls and work practices to reduce exposures to or below the PELs, and when those controls cannot achieve the PELs, use them to reduce exposure as far as possible and supplement them with respirators. These duties are described in 1910.1051(f)(1)(i)–(ii). Employers must therefore prioritize ventilation, enclosure, and process changes, and only rely on respirators when controls alone are insufficient.

A written compliance plan is required whenever any employee exposures are over the PELs, and it must focus on reducing exposures primarily through engineering and work practices, include a schedule for implementation and leak detection surveys, be available for inspection, be reviewed at least every 12 months, and not use employee rotation as a compliance method. These requirements are in 1910.1051(f)(2)(i)–(iv). Keep copies ready for the Assistant Secretary, the Director, and affected employees or their representatives.

An exposure goal program must be implemented for operations or job classifications where exposures exceed the action level, and it should include measures intended to keep exposures below the action level during normal operations. The requirement is in 1910.1051(g)(1). Core elements to include are a leak prevention/detection/repair program, maintenance for local exhaust ventilation, use of pump exposure-control technology, gauging devices that limit exposure, unloading devices like vapor return systems, and control room measures as described in 1910.1051(g)(5).

Respirators are required when they are necessary during periods to install engineering controls, for infrequent non‑routine tasks of limited duration, for operations where feasible controls can't yet reduce exposure to or below the PELs, and in emergencies. These situations are listed in 1910.1051(h)(1)(i)–(iv). Employers must provide appropriate respirators and implement a respirator program per 1910.1051(h)(2).

If air‑purifying respirators are used, employers must replace filter elements at the schedule in Table 1 and at the start of each shift, or may replace at 90% of service life if they can demonstrate protection using worst‑case BD breakthrough data and document the basis; each element must be labeled with the date/time first installed. These rules are in 1910.1051(h)(2)(ii)–(iv). If a NIOSH‑approved end‑of‑service‑life indicator exists, it may be used per 1910.1051(h)(2)(v).

The employer must replace the air‑purifying filter element immediately if an employee detects the odor of BD, regardless of the element type. This immediate replacement requirement is in 1910.1051(h)(2)(vi). Employers should have procedures for prompt replacement and remove the employee from exposure until replacement is complete.

Employers must select respirators that meet the minimum types listed in Table 1 for the measured BD concentration or condition of use and follow the cartridge‑replacement intervals in that table. The selection guidelines appear in 1910.1051(h)(3)(i) and Table 1 of the standard. For example, up to 5 ppm requires air‑purifying half or full facepiece with BD/organic vapor cartridges replaced every 4 hours, and higher concentrations require full facepieces, PAPRs, or supplied‑air systems as specified in Table 1.

Air‑purifying respirator filter elements must be NIOSH‑approved for organic vapors or BD, and if an employee cannot use a negative‑pressure respirator, the employer must provide a lower‑breathing‑resistance alternative (like a PAPR or supplied‑air) that gives adequate protection. These requirements are in 1910.1051(h)(3)(ii)–(iii). Employers must document selection and provide fit testing and training under the respiratory program in 1910.1051(h)(2).

A full facepiece respirator is required whenever eye irritation is anticipated or when Table 1 specifies a full facepiece for the concentration range; the standard explicitly notes that a full facepiece is required when eye irritation is anticipated. See 1910.1051(h)(3) and the accompanying Table 1. Employers should evaluate potential eye exposures and choose facepieces accordingly, and ensure eye/face protection meets 1910.133 when appropriate.

The employer must provide, at no cost, protective clothing and equipment to prevent eye contact and limit dermal exposure to BD whenever it is appropriate for protection, and ensure its use; eye and face protection must meet [1910.133]. This duty is stated in 1910.1051(i). Employers should assess tasks for skin and eye exposure potential and supply chemical‑resistant gloves, suits, goggles, or face shields as needed.

Employers must prepare or adapt a written emergency plan that contains applicable elements of [1910.38], [1910.39], and [1910.120], and must institute medical screening and surveillance for employees meeting the exposure thresholds described in [1910.1051(k)(1)]. The emergency plan requirement is in 1910.1051(j) and the medical surveillance coverage rules are in 1910.1051(k)(1). Medical surveillance applies to employees exposed at or above the action level on 30+ days or at/above PELs on 10+ days per year, to those with significant past exposures, and to those exposed after an emergency.

Employers (including successor owners) must continue medical screening and surveillance for employees whose work histories show specified past exposure patterns, such as exposures at or above the PELs on 30+ days per year for 10+ years, or at or above the action level on 60+ days per year for 10+ years, or above 10 ppm on 30+ days in any past year. These continuation rules are in 1910.1051(k)(1)(ii). Employers must track work histories and maintain surveillance even after employees transfer to non‑BD jobs.

The compliance plan schedule must cover development and implementation of engineering and work practice controls and include periodic leak detection surveys. This scheduling requirement is in 1910.1051(f)(2)(ii). The schedule should set realistic dates, responsible parties, and milestones for leak detection, repair, ventilation upgrades, and other control measures.

No — the employer shall not implement a schedule of employee rotation as a means of complying with the PELs. That prohibition is explicit in 1910.1051(f)(2)(iv). Employers must control exposures through engineering, work practices, and respiratory protection where permitted.

Employers should use pump exposure‑control technologies (e.g., mechanical double‑sealed or seal‑less pumps), gauging devices that limit exposure (such as magnetic gauges on rail cars), and unloading devices designed to limit exposure (for example, vapor return systems). These suggested measures are listed in 1910.1051(g)(5)(iii)–(v). Implementing these controls is part of an exposure goal program intended to keep concentrations below the action level during normal operations.

If using a 90% service‑life replacement schedule instead of Table 1, the employer must demonstrate that employees are adequately protected by that procedure and must use BD breakthrough data derived from tests under worst‑case humidity, temperature, and airflow conditions; the employer must describe and document the supporting data and the basis for using it in the respirator program. These requirements are in 1910.1051(h)(2)(iii)(A)–(B). Keep the documentation with the respirator program records and make it available for review.

At BD concentrations up to 25 ppm, acceptable options include a full facepiece air‑purifying respirator with BD or organic vapor cartridges replaced every 2 hours; a powered air‑purifying respirator (PAPR) with approved cartridges replaced every 2 hours; or a continuous‑flow supplied‑air respirator with a hood or helmet. These options are given in Table 1 and 1910.1051(h)(3)(i). Employers must also ensure the chosen respirator is part of a compliant program per 1910.1051(h)(2).

For conditions with BD greater than 1000 ppm, unknown concentrations, or firefighting, the standard requires a self‑contained breathing apparatus (SCBA) with a full facepiece operated in pressure‑demand or other positive‑pressure mode, or a supplied‑air respirator with full facepiece in pressure‑demand mode in combination with an auxiliary SCBA; these are specified in Table 1 and 1910.1051(h)(3). Employers must treat these conditions as IDLH and ensure emergency procedures per 1910.1051(j).

Yes — under 1910.1051(k)(2)(i) the employer must ensure the health questionnaire, physical examination and medical procedures are provided without cost to the employee, without loss of pay, and at a reasonable time and place (1910.1051(k)(2)(i).

• Medical services must also be performed by an appropriate professional: see 1910.1051(k)(2)(ii) requiring a physician or other licensed health care professional, and laboratory tests must be done by an accredited lab per 1910.1051(k)(2)(iii).

• Practical tip: schedule screenings during work hours when possible and document that employees incurred no loss of pay.

Employees covered under paragraphs (j)(1)(i)-(ii) must be offered a health questionnaire and a complete blood count (CBC) with differential and platelet count every year; physical examinations are required at specific times as described in the standard (1910.1051(k)(3)(i).

• Physical exam timing details: initial exam if 12 months or more have passed since the last program exam (1910.1051(k)(3)(i)(A)); before assignment to a BD-exposure job (1910.1051(k)(3)(i)(B)); every 3 years after the initial exam (1910.1051(k)(3)(i)(C)); at physician discretion (1910.1051(k)(3)(i)(D)); on reassignment out of BD exposure when appropriate (1910.1051(k)(3)(i)(E)); and at termination if 12 months have elapsed since the last exam (1910.1051(k)(3)(i)(F)).

• Keep records of scheduling and results so you can demonstrate compliance with the annual CBC and the physical exam timing requirements.

After an emergency BD exposure the employer must arrange medical screening as quickly as possible, and no later than 48 hours after exposure; at minimum this must include a CBC within 48 hours and then monthly for three months, plus a physical exam if the employee reports specific acute symptoms (1910.1051(k)(3)(ii) and 1910.1051(k)(4)(ii).

• The physical exam is required if the employee reports irritation of eyes, nose, throat, lungs, or skin, blurred vision, coughing, drowsiness, nausea, or headache (1910.1051(k)(4)(ii)).

• The physician may extend surveillance beyond the minimum if clinically warranted; document timing and results to show the 48-hour CBC and the monthly follow-ups were provided.

The medical screening program must include a baseline health questionnaire (updated annually), a complete physical exam emphasizing liver, spleen, lymph nodes, and skin, a CBC, and any other tests the examining physician deems necessary (1910.1051(k)(4)(i)(A)-(D)).

• The baseline health questionnaire must be the sample form in appendix C or equivalent and emphasize hematopoietic and reticuloendothelial systems and other chemical exposures (1910.1051(k)(4)(i)(A)).

• Include documentation of the CBC results and any additional tests the clinician orders; retain summaries consistent with the standard's recordkeeping requirements.

The employer must provide the physician or licensed health care professional a copy of the BD standard and appendices, a description of the employee's duties related to BD exposure, the employee's actual or representative BD exposure levels (including during emergencies), a description of pertinent PPE used, and available prior employment-related medical evaluations (1910.1051(k)(6)).

• These items are listed specifically at 1910.1051(k)(6)(i)-(v).

• Practical step: prepare a concise packet for the clinician that includes a copy of the standard, a job description, recent exposure measurements, PPE list, and prior medical summaries to speed accurate evaluation.

The examining physician or licensed health care professional must produce a written opinion within 15 business days of the evaluation that includes the occupationally pertinent results, a medical opinion about any detected conditions that increase the risk of material health impairment from BD, recommended exposure limitations, and a statement that the employee was informed of the results; the opinion must not disclose unrelated diagnoses (1910.1051(k)(7) and 1910.1051(k)(7)(i)-(ii)).

• Specifically see required items at 1910.1051(k)(7)(i)(A)-(D).

• Note: The physician may still inform the employee directly of other adverse findings even if those findings are not in the written opinion to the employer (1910.1051(k)(7)(ii)).

Information from medical screening must be aggregated without personal identifiers and periodically reviewed for employee population effects, and individual medical information must be kept confidential while still being disseminated to covered employees in a way that protects privacy (1910.1051(k)(8) and 1910.1051(k)(8)(ii).

• Employees exposed at or above the action level or STEL must receive training per the Hazard Communication Standard (1910.1051(l)(2)) and be informed of the right to obtain medical exams at no cost, their medical records required under the standard (1910.1051(l)(2)(iv)(F)(1)-(2)), and air monitoring results (1910.1051(l)(2)(iv)(F)(3)).

• Employers must also make the BD standard and appendices readily available to employees and representatives (1910.1051(l)(3)(i)-(ii)).

If an employee must wear a respirator, the employer must ensure a medical determination of the employee's physical ability to perform the work and use the respirator as required by 29 CFR 1910.134 (1910.1051(k)(3)(iii) and 1910.134).

• Follow the medical evaluation procedures in 1910.134 (medical questionnaire or examination, follow-up exams, and written medical clearance) to ensure employees can safely wear respirators while performing BD-related tasks.

• Keep documentation of respirator medical clearances and any work limitations provided by the clinician.