Common Errors in Gas Detector Calibration
Gas detector calibration is the process of adjusting a detector’s readings by comparing them to a more accurate, traceable reference gas so results are trustworthy for safety and compliance. In Australia, auditors expect ISO/IEC 17025 traceability on certificates from NATA-accredited providers.
What is Gas Detector Calibration?
Calibrating a gas detector sets its zero and span so it reads the right value when exposed to a known gas. In Australia that means using correct gas, flow and procedure, recording results, and keeping NATA-endorsed evidence that’s traceable to national standards. Many sites require a daily bump test and monthly quarterly calibrations, driven by risk and manufacturer instructions.
Why Calibration Matters in Australia
WHS laws place a duty on PCBUs to manage risks. Approved Codes of Practice (confined spaces; hazardous chemicals) outline practical testing steps and sampling methods; following them is an accepted way to meet the Regulations. Confined-space mis-testing can be fatal. Safe Work Australia’s 2025 release confirms 188 traumatic injury fatalities in 2024 regulators scrutinise plant safety records and evidence of control.
The Most Common Calibration Errors
Below are the failure modes we see across labs, plants and field teams in Australia and how to fix them.
1) Skipping bump tests before use
Symptom: Detector “works on paper” but doesn’t alarm to gas on shift.Cause: No functional challenge before entry.Fix: Enforce a pre-use bump test (or before each shift). Use docking stations to automate tests, logs and certificates.
2) Using expired or incorrect calibration gas
Symptom: Readings drift after “successful” calibration.Cause: Expired cylinders; wrong balance gas (air vs N₂) or wrong concentration. Reactive mixes (e.g., H₂S, Cl₂) can change over time.Fix: Track expiry and lot; match gas matrix and set-point to the sensor spec; store cylinders correctly.
3) Wrong flow rate or regulator type
Symptom: Slow or unstable response; calibration won’t settle.Cause: Using a fixed-flow regulator on a pumped instrument (or vice-versa), or using the wrong flow.Fix: For pumped instruments use a demand-flow regulator; for diffusion instruments, a fixed-flow set to the manufacturer-specified rate. Verify flow with a calibrator.
4) Calibrating in unsuitable environments
Symptom: Results vary between benches or between days.Cause: Wind, heat, humidity; silicone/solvent vapours; nearby sources of contaminants.Fix: Calibrate in a clean, ventilated spot; allow temperature stabilisation; keep silicones, solvents and aerosols away, these can poison catalytic LEL sensors.
5) Poor zero/span procedure
Symptom: Zero offsets; overshoot; inconsistent span.Cause: No warm-up; skipping fresh-air zero; not waiting for stable readings.Fix: Standardise the SOP: warm-up, fresh-air zero, span at the correct flow until stable, document acceptance ranges. Docking systems help make steps repeatable.
6) Confusing %LEL with ppm
Symptom: Wrong alarm set-points on multi-gas units; flammables checked in ppm charts, toxics in %LEL by mistake.Cause: Unit mix-ups %LEL is for flammability, ppm is typical for toxic gases.Fix: Put the units on the work instruction, and validate alarms after calibration.
7) Ignoring cross-sensitivity & sensor poisoning
Symptom: CO alarms in battery rooms; PID VOC readings in solvent-rich air are “too high.”Cause: Non-target gases affect the sensor (e.g., H₂ interferes with CO); silicones/lead/sulphur can poison pellistors. Fix: Check the maker’s cross-sens tables; choose filtered or H₂-compensated sensors; verify with the correct target gas.
8) Not updating intervals after sensor replacement or harsh exposure
Symptom: Fresh sensor drifts early; over-range exposure followed by quiet failures.Cause: Intervals remain “business as usual” after a change-out, shock, poisoning or over-range event.Fix: Shorten intervals temporarily and re-establish stability; record the trigger in the asset system.
9) Inadequate record-keeping & traceability
Symptom: Audit failures; “no evidence” of calibration, gas lot, or uncertainty.Cause: Paper logbooks only; no NATA-endorsed reports; missing gas details.Fix: Keep certificates with as-found/as-left, uncertainty, reference IDs and NATA traceability; use docking stations/portals for automated logs.
10) Relying on non-accredited providers
Symptom: Certificates rejected by clients or regulators.Cause: Results not issued under ISO/IEC 17025; no evidence of SI traceability.Fix: Use a NATA-accredited lab to check the scope and the endorsement.
11) No confined-space pre-entry test plan
Symptom: Atmosphere tested only at head height or after entry.Cause: No plan for remote sampling, top-middle-bottom stratification, and continuous monitoring.Fix: Follow the Model Code of Practice Confined Spaces and your jurisdiction’s code.
Consequences of Calibration Errors
Safety: False negatives or false positives in confined spaces expose workers to toxic or flammable atmospheres. The Confined Spaces Code sets expectations for testing and monitoring methods.
Compliance: Poor practice can trigger improvement notices or stop-work orders; inspectors expect traceable, competent calibrations and pre-entry testing.a
Operations: Downtime and rework add cost. National WHS statistics underline the scale of harm and the scrutiny on plant-related risks.
Australian Standards, Codes & Frequency Guidance
AS/NZS 60079.29.2: selection, installation, use and maintenance of flammable-gas and oxygen detectors (your go-to maintenance reference).
AS/NZS 60079.29.1: performance requirements for flammable-gas detectors (equipment performance).
Model Code of Practice confined Spaces: test from outside, sample different levels, and keep monitoring while occupied (updated Nov 2024).
Managing risks of hazardous chemicals: approved code that explains how codes support WHS duties.
Frequency: standards and codes set methods and duties, not fixed intervals. Intervals are risk-based and guided by manufacturer instructions and use conditions.
How to get Calibration Right (Step-by-step)
Check environment & gas: Choose a clean area; confirm cylinder concentration, balance gas, lot & expiry; consider temperature.
Inspect the instrument: Battery, filters, sample lines, pump (if fitted).
Fresh-air zero & warm-up: Stabilise, then zero in clean air.
Bump test: Challenge all sensors; confirm alarms/response time before calibration.
Apply span gas correctly: Use the right regulator type/flow; wait for a stable span at each point.
Save results: Store as-found/as-left, uncertainty, gas lot/expiry, and technician ID on a NATA-endorsed certificate (or in your dock).
Verify: Run a post-cal bump or check.
Set next due date: Base it on risk, use and any recent events (over-range, shock, replacement).
Choosing a NATA-accredited Provider
Look for: a NATA scope covering gas detectors; ISO/IEC 17025 endorsement on reports; uncertainties on the certificate; practical turnaround; onsite vs lab options; digital records/portal. CISCAL holds continuous ISO/IEC 17025 accreditation through NATA (Acc. No. 411), covers NSW/VIC/QLD with reach across Australia and the Pacific, and provides the SMART Portal for real-time job tracking and asset/certificate management.