Hearing conservation definitions

Under 1910.95 App I the "Action level" is an 8-hour time-weighted average of 85 decibels (A-weighted, SLOW response) or equivalently a noise dose of fifty percent. Employers must use this Action level to determine when to implement a hearing conservation program and when to begin monitoring and audiometric testing under 1910.95(c) and the Appendix I definitions.

• Use the Action level (85 dBA TWA or 50% dose) to decide when employees need baseline audiograms, training, and hearing protection.`

(See 1910.95(c) and Appendix I to 1910.95.)

An audiogram is a chart, graph, or table showing an individual’s hearing threshold levels across frequencies as produced by an audiometric test. Employers use audiograms for baseline and periodic hearing tests required by the hearing conservation provisions in 1910.95(g) and the term is defined in Appendix I to 1910.95.

• Baseline and subsequent audiograms let you compare hearing over time and detect standard threshold shifts.

(See 1910.95(g) and Appendix I to 1910.95.)

An "Audiologist" under 1910.95 App I is a professional specializing in the study and rehabilitation of hearing who is certified by the American Speech-Language-Hearing Association or licensed by a state board of examiners. Employers must use qualified professionals for audiometric programs as described in 1910.95(g) and the definition appears in Appendix I to 1910.95.

• If you contract out testing, ensure the provider meets this certification or licensing definition so baseline and follow-up audiograms are valid.

(See 1910.95(g) and Appendix I to 1910.95.)

A baseline audiogram is the audiogram against which future audiograms are compared. Employers must obtain a valid baseline for each employee exposed at or above the Action level so subsequent audiograms can be compared to detect any hearing change under 1910.95(g) and the term is defined in Appendix I to 1910.95.

• A good baseline is taken under quiet conditions and before significant work exposure, or after appropriate hearing protector attenuation is accounted for.

(See 1910.95(g) and Appendix I to 1910.95.)

The "Criterion sound level" under 1910.95 App I is defined as 90 decibels. OSHA uses this 90 dB level as the reference (criterion) level when determining permissible exposure and calculating noise dose under the standard; see 1910.95 and the Appendix I definitions.

• The 90 dB criterion is central to the noise dose math in the standard; hearing conservation actions use the 85 dB Action level while the criterion supports dose calculations and permissible limits.

(See 1910.95 and Appendix I to 1910.95.)

A decibel (dB) is the unit of measurement for sound level. For use with the hearing conservation standard, measurements must be A-weighted and use SLOW time response as required by Appendix I to 1910.95 and applied within 1910.95.

• "A-weighted" accounts for human ear sensitivity across frequencies; "SLOW" response follows ANSI S1.4-1971 (R1976) as noted in the Appendix.

(See Appendix I to 1910.95 and 1910.95.)

Under 1910.95 App I, a Hertz (Hz) is the unit of frequency equal to cycles per second. Hertz matter for audiograms because hearing thresholds are reported across a range of frequencies (Hz) to show where hearing loss occurs; see Appendix I to 1910.95 and 1910.95(g).

• Typical audiograms plot thresholds at standard frequencies (e.g., 500, 1000, 2000, 3000, 4000 Hz) to detect work-related shifts.

(See Appendix I to 1910.95 and 1910.95(g).)

Under 1910.95 App I, "Medical pathology" means a disorder or disease affecting the ear that should be treated by a physician specialist. Employers must refer employees for medical evaluation when audiometric or other indicators suggest a medical pathology; see Appendix I to 1910.95 and the audiometric provisions in 1910.95(g).

• If an audiologist or physician suspects a medical condition (e.g., middle ear disease), timely medical follow-up is required to rule out non-occupational causes or treatable conditions.

(See Appendix I to 1910.95 and 1910.95(g).)

Under 1910.95 App I, "Noise dose" is the percentage ratio of the time-integrated, 0.6 power of the measured SLOW A-weighted sound pressure over a specified period to the product of the criterion duration (8 hours) and the 0.6 power of the squared sound pressure at the 90 dB criterion. In plain terms, noise dose quantifies how much of the allowable daily noise exposure an employee receives and is used to determine compliance and the need for hearing conservation measures; see Appendix I to 1910.95 and exposure monitoring rules in 1910.95(c).

• A dose of 100% equals the full 8-hour exposure at the 90 dB criterion; a 50% dose (the Action level) corresponds to an 8-hour TWA of 85 dBA.

(See Appendix I to 1910.95 and 1910.95(c).)

A "Noise dosimeter" is an instrument that integrates a function of sound pressure over time so it directly indicates a noise dose. Employers should use noise dosimeters to measure an individual employee’s dose during a work shift or task to determine whether the Action level or permissible exposures are exceeded, per Appendix I to 1910.95 and monitoring requirements in 1910.95(c).

• Dosimeters are practical for personal monitoring (wearing on the shoulder) when workers move among noise sources.

(See Appendix I to 1910.95 and 1910.95(c).)

An "Otolaryngologist" under 1910.95 App I is a physician specializing in diagnosis and treatment of ear, nose and throat disorders. Employers should involve an otolaryngologist when audiometric results or medical evaluations indicate conditions requiring physician diagnosis or treatment beyond what an audiologist provides; see Appendix I to 1910.95 and the medical follow-up provisions in 1910.95(g).

• Use an otolaryngologist for suspected medical pathologies or when employee care needs physician-level intervention.

(See Appendix I to 1910.95 and 1910.95(g).)

Under 1910.95 App I, a "Representative exposure" is a measurement of an employee’s noise dose or 8-hour TWA that the employer considers to represent exposures of other employees in similar jobs or areas. Employers may use representative exposures for groups of employees when it reasonably reflects others’ exposures for monitoring and program decisions under 1910.95(c) and the Appendix I definition.

• Representative monitoring is allowed when tasks, tools, and environments are substantially the same; document how the measurements represent the group.

(See 1910.95(c) and Appendix I to 1910.95.)

Under 1910.95 App I, "Sound level" is ten times the common logarithm of the ratio of the square of the measured A-weighted sound pressure to the square of the 20-micropascal reference pressure, reported in decibels; for the regulation you must use A-weighting and SLOW time response in accordance with ANSI S1.4-1971 (R1976). This definition and measurement requirement are in Appendix I to 1910.95 and apply when determining exposures under 1910.95.

• Always record measurements with A-weighting and SLOW response as required by the Appendix to ensure compliance and comparability.

(See Appendix I to 1910.95 and 1910.95.)

A "Sound level meter" under 1910.95 App I is an instrument for measuring sound level (instantaneous levels). Use a sound level meter when you need spot measurements, area surveys, octave-band or frequency-specific readings, or to check specific sources; use a noise dosimeter when you need an integrated personal dose over a work shift. See Appendix I to 1910.95 and monitoring guidance in 1910.95(c).

• Sound level meters are ideal for mapping noise, while dosimeters are best for personal exposure assessments.

(See Appendix I to 1910.95 and 1910.95(c).)

Under 1910.95 App I, the "Time-weighted average sound level" is the constant sound level over an 8-hour exposure that would result in the same noise dose as the measured variable exposure. An 8-hour TWA of 85 dBA equals the Action level (50% dose) used to trigger hearing conservation measures; see Appendix I to 1910.95 and exposure rules in 1910.95(c).

• Convert variable exposures to an 8-hour TWA to compare with the 85 dBA Action level and other limits.

(See Appendix I to 1910.95 and 1910.95(c).)

Under 1910.95 App I employers must use A-weighting and SLOW time response when measuring sound levels for purposes of the hearing conservation standard; the Appendix specifically requires SLOW response in accordance with ANSI S1.4-1971 (R1976) and A-weighting for measurements used in the standard. See Appendix I to 1910.95 and the overall standard 1910.95.

• Ensure sound level meters and dosimeters are set to A-weighting and SLOW response before taking compliance measurements.

(See Appendix I to 1910.95 and 1910.95.)

Under 1910.95 App I employers may rely on representative exposure measurements to represent groups of employees when those measurements reasonably reflect the exposures of others doing the same tasks; the Appendix defines "Representative exposure" and 1910.95(c) governs monitoring decisions. Employers should document why the measurements are representative (similar tasks, equipment, duration, and locations) and retain records as required.

• Document sampling methods, locations, job tasks, and reasoning that exposures are comparable to support program decisions.

(See Appendix I to 1910.95 and 1910.95(c).)

Under 1910.95 App I a dose of fifty percent means the employee received half of the allowable daily noise dose—equivalently an 8-hour time-weighted average of 85 dBA (the Action level). Employers use this threshold to trigger hearing conservation actions such as audiometric testing and training in 1910.95(c) and the Appendix definitions.

• Practically, if a worker’s measured noise dose reaches 50% during a shift, the employer must implement the hearing conservation program requirements tied to the Action level.

(See Appendix I to 1910.95 and 1910.95(c).)

Under 1910.95 App I employers calculate an 8-hour TWA by integrating the measured A-weighted, SLOW sound pressure (or using a dosimeter that applies the standard’s dose algorithm) so that the variable exposure is converted into the equivalent constant level over 8 hours; the Appendix gives the noise dose mathematical basis and monitoring obligations in 1910.95(c).

• Use a properly calibrated dosimeter set to A-weighting and SLOW to directly get dose or compute TWA from measured levels and durations; follow the Appendix formula for consistency.

(See Appendix I to 1910.95 and 1910.95(c).)

Under 1910.95 App I the 90 dB criterion is the reference level used to compute noise dose, but hearing protection requirements depend on the Action level and employer program obligations: the hearing conservation program is triggered at an 85 dBA TWA (Action level), and 1910.95(e) covers hearing protectors and when employers must provide them. In short, the 90 dB criterion is used in dose math while the Action level (85 dBA) is the practical threshold for starting conservation actions and providing protection.

• Employers must provide hearing protectors and training when employees are at or above the Action level (85 dBA TWA), and may require them at higher levels per the employer’s exposure control policy.

(See Appendix I to 1910.95 and 1910.95(e).)