How Calibration Services Keep Occupational Health Equipment Reliable

What does a calibration service actually check?

A calibration service compares an instrument's output against a certified reference standard with known, traceable accuracy, then adjusts or documents any deviation. For an audiometer, that means verifying the sound pressure levels produced at each test frequency against a calibrated sound level meter and coupler, following ANSI S3.6. For a spirometer, it means running certified calibration syringes through the device to confirm volume and flow accuracy against ATS criteria. For a breath alcohol testing (BAT) instrument, it means checking the device's reading against a certified wet bath simulator or dry gas standard at a known alcohol concentration. In every case, the goal is the same: prove the number the instrument reports matches a known reference, not just that the instrument powers on and runs.

How often does occupational health equipment need calibration?

Intervals depend on the instrument and the standard governing it, not a single company-wide schedule. Audiometers used for OSHA hearing conservation programs need a functional check before each day's testing and an acoustic calibration at least annually, plus an exhaustive calibration (checking every specification against ANSI S3.6) every two years. Breath alcohol testing devices require an accuracy check on a schedule set by the manufacturer and 49 CFR Part 40, typically at intervals ranging from every 10-14 days to every 6 months depending on the specific EBT model. Spirometers need calibration verification at minimum daily during use, per ATS/ERS guidance. Treating all instruments on one blanket "annual calibration" schedule is a common gap we find during program audits — it satisfies none of the individual standards correctly.

Instrument	Governing standard	Typical interval
Audiometer (functional check)	29 CFR 1910.95	Daily, before testing
Audiometer (acoustic calibration)	ANSI S3.6	Annual
Audiometer (exhaustive calibration)	ANSI S3.6	Every 2 years
Breath alcohol EBT device	49 CFR Part 40	Manufacturer-specific, 10 days-6 months
Spirometer	ATS/ERS guidance	Daily verification during use

What makes a calibration certificate defensible?

A defensible calibration certificate documents the instrument's serial number, the date of calibration, the reference standard used and its own traceability (typically to NIST), the as-found and as-left readings at each test point, and the technician's identity and credentials. Without as-found readings, there's no record of whether the instrument was drifting out of tolerance before adjustment — information that matters if a past test result is ever challenged. A certificate that only states "calibrated and passed" without the underlying data doesn't hold up the same way under audit or in a dispute, because it gives no way to evaluate whether the instrument was actually within spec at the time it was used.

Why does NIST traceability matter for compliance?

NIST traceability means the reference standard used to calibrate an instrument can be linked, through an unbroken chain of comparisons, back to a national measurement standard maintained by the National Institute of Standards and Technology. This chain is what allows an auditor, a court, or another lab to trust that "calibrated" means something consistent across different service providers, rather than each vendor calibrating against its own uncontrolled reference. For OSHA-regulated hearing conservation and DOT-regulated alcohol testing programs specifically, calibration records without demonstrable traceability are a common finding in program audits, since the standard itself typically requires it even when not spelled out in exact NIST language.

How Foster handles calibration across mixed equipment fleets

Foster calibrates audiometers, spirometers, sound level meters, dosimeters, and breath alcohol devices on their own governing schedules rather than a single blanket interval, and every certificate we issue includes as-found and as-left readings tied to NIST-traceable references. For clients running audiometric and BAT programs together, we've found the biggest operational risk isn't any single instrument falling out of calibration — it's a fleet where different equipment types are tracked in different systems (or not tracked at all), so a lapsed calibration goes unnoticed until an audit or an incident forces the question. Our on-site and mail-in calibration services build a single tracking calendar across every instrument type a client runs, so the audiometer's annual and the BAT device's 30-day check don't live in separate spreadsheets nobody reconciles. See our calibration services page for turnaround times and supported instrument models.

FAQ

Can an instrument fail calibration and still be used?

No. If as-found readings show the instrument is outside tolerance, it needs adjustment and re-verification before returning to service. Using an out-of-tolerance instrument for compliance testing risks invalidating the results it produces, which is the underlying reason the as-found/as-left documentation matters.

Does calibration extend an instrument's usable life?

Regular calibration doesn't repair mechanical wear, but it catches drift before it becomes a functional failure, and the underlying maintenance check performed alongside calibration (connector wear, battery health, sensor condition) often surfaces issues that would otherwise cause an unplanned breakdown. It's a diagnostic checkpoint as much as an accuracy correction.

Who is qualified to perform calibration on occupational health instruments?

Requirements vary by instrument and standard. Audiometer calibration should be performed by a technician trained on the relevant ANSI standards; BAT device accuracy checks require the calibration to follow the specific manufacturer's protocol referenced in the device's DOT approval. See our BAT training program and hearing testing services for how Foster trains and calibrates together.

What happens if calibration records are missing during an OSHA inspection?

Missing or incomplete calibration records are a common citable finding, since the underlying testing program standard (1910.95 for audiometry, for example) requires the equipment to be calibrated, and the employer bears the burden of proving it was. Related: our post on audiometer exhaustive calibration requirements covers the specific ANSI S3.6 checkpoints an inspector may ask about.

How do I get a calibration quote for a mixed fleet of instruments?

Request a quote through our quote page with your instrument list and current calibration dates, and we'll build a consolidated schedule rather than quoting each device type separately.