Calibration gas is a precisely manufactured gas mixture of a known concentration, used to calibrate and bump test gas detectors so their readings stay accurate. This guide covers what calibration gas is, the difference between span gas and zero gas, balance gases, tolerance, and why NIST traceability matters.
What is calibration gas?
Gas sensors drift over time. Calibration gas gives the instrument a reference point of exactly known concentration so it can be adjusted to read correctly. Each cylinder is filled to a target value (for example, 25 ppm hydrogen sulfide) within a stated tolerance and ships with a NIST-traceable Certificate of Analysis.
Span gas vs. zero gas
- Span gas is the mixture containing the target gas at a known concentration. It sets the detector's "span" — its reading at a meaningful, above-alarm level.
- Zero gas contains none of the target gas (clean air or pure nitrogen). It sets the detector's baseline, or "zero." Zero air (20.9% O2, balance nitrogen, hydrocarbon-free) is the most common zero gas.
A full calibration uses both: zero first to set the baseline, then span to set the response.
Balance gas: air vs. nitrogen
The target gas makes up a tiny fraction of the cylinder; the rest is a balance gas, usually air or nitrogen. Reactive gases and many toxic mixes use a nitrogen balance for stability; oxygen-deficiency and some combustible mixes use an air balance. The correct balance is specified per application — it is listed on every Trigas USA product.
Tolerance and NIST traceability
Tolerance is how close the actual fill is to the labeled value (for example ±2% or ±5%). NIST-traceable certification means the analysis is referenced to national standards, which is what auditors and EHS programs expect. Single-component gases (one target gas) and multi-gas mixes such as 4-gas quad mixes are both available.
Single-gas vs. multi-gas mixes
Use a single-gas cylinder (for example carbon monoxide or hydrogen sulfide) to calibrate one sensor, or a multi-gas mix to calibrate a 4-gas confined-space monitor in one step. Need to match an OEM part number? Use our cross-reference.
Browse calibration gas by gas type →
Every Trigas USA cylinder is NIST-traceable with an ISO 17025 CoA, 15–30% below OEM, shipped in 48 hours from Florida.
Frequently asked questions
What is the difference between span gas and zero gas?
Span gas contains a known concentration of the target gas to set the detector's response; zero gas contains none of it to set the baseline.
What balance gas should calibration gas use?
Air or nitrogen, depending on the application. Reactive and many toxic mixes use nitrogen; oxygen and some combustible mixes use air.
What does tolerance mean on calibration gas?
It is how close the actual fill is to the labeled concentration, e.g. ±2% or ±5%.