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Overview
In gas detection, calibration is not a formality — it is the verification step that determines whether a detector will protect the worker using it. A four-gas monitor that has not been bump tested or calibrated with the correct certified span gas cannot be confirmed to alarm at the right concentrations in the field. For industries where gas hazards are routine and confined space entry is part of daily operations, that uncertainty is not acceptable. The 4-MIX span gas cylinder — CO 50ppm, H2S 25ppm, CH4 2.5% / 50% LEL, O2 12%, Balance Nitrogen is a certified four-gas calibration mixture formulated for operations where Methane is the correct LEL calibration reference, CO alarm response needs to be verified at the lower 50ppm range, and oxygen sensor performance needs to be confirmed against a severely depleted atmosphere.
Available in cylinder sizes from 34 litres to 116 litres, this mixture is used to bump test and calibrate portable four-gas monitors across natural gas operations, marine enclosed space entry, offshore platforms, petrochemical facilities, and industrial confined space programmes where the detector manufacturer specifies Methane as the factory calibration gas and where the specific concentration combination of this mixture aligns with the instrument’s calibration standard.
What distinguishes this mixture from a standard four-gas span gas cylinder is the combination of CH4 at 50% LEL and O2 at 12% vol. The Methane LEL concentration is the correct calibration reference for instruments factory-calibrated to CH4 — which includes the majority of portable four-gas monitors used in natural gas, upstream oil and gas, and utility applications. The 12% oxygen concentration — significantly below the 19.5% oxygen-deficient atmosphere threshold — verifies that the O2 sensor responds correctly across the lower end of the depletion range, not just at the alarm trigger point. For procurement teams sourcing the right span gas for a Methane-calibrated detector fleet with demanding oxygen monitoring requirements, this cylinder provides both the correct LEL reference and the more rigorous O2 sensor verification in a single four-gas mixture.
Key Features
Methane (CH4) at 2.5% / 50% LEL — Correct LEL Reference for Natural Gas and Methane-Calibrated Detectors
Methane is the most widely used calibration gas for LEL sensors in portable four-gas monitors, and it is the factory calibration reference for the majority of instruments used in natural gas distribution, upstream oil and gas, and utility confined space entry programmes. At 2.5% by volume — equivalent to 50% of Methane’s lower explosive limit of 5% — this concentration provides a mid-range calibration point that verifies sensor linearity and confirms alarm response across the operational detection range. For teams operating CH4-calibrated instruments in natural gas environments, using Methane span gas provides a direct calibration reference that accurately represents the actual combustible gas hazard, rather than a surrogate gas with different response characteristics.
CO at 50ppm — Lower-Range Carbon Monoxide Sensor Verification
Carbon monoxide at 50ppm — rather than the 100ppm calibration point used in many general-purpose four-gas span gas mixtures — is the calibration concentration specified by certain detector manufacturers for instruments with CO alarm thresholds set at 35ppm TWA and 200ppm STEL. Calibrating at 50ppm places the verification point above the TWA alarm threshold and confirms sensor sensitivity in the range immediately above where the first CO alarm should trigger. This is the more relevant calibration point for environments where low-level CO exposure from combustion equipment, diesel exhaust, or partial oxidation processes is the primary worker health risk — where confirming that the sensor responds correctly just above the action level matters more than verifying a high-concentration response.
H2S at 25ppm — Industry-Standard Hydrogen Sulphide Calibration Concentration
Hydrogen sulphide at 25ppm is the standard calibration concentration for H2S sensors in portable four-gas instruments across the safety industry. The 25ppm point sits above the OSHA ceiling limit of 20ppm and confirms that the sensor can detect and alarm at concentrations in the immediately hazardous range. For oil and gas, marine, wastewater, and confined space operations where H2S is a routine hazard, bump testing with a certified H2S calibration gas is the only way to confirm the sensor has not drifted below its alarm threshold response level before a worker enters a potentially H2S-contaminated space.
O2 at 12% Vol — Severely Depleted Oxygen Atmosphere Verification
The oxygen concentration in this mixture at 12% vol is well below the 19.5% OSHA oxygen-deficient atmosphere threshold and significantly below the 16% level at which cognitive impairment begins in most workers. Verifying the O2 sensor against a 12% atmosphere confirms sensor response across the lower range of oxygen depletion — not just at the alarm trigger point. This is particularly relevant for enclosed space entry on vessels where inert gas systems are in use, for natural gas pipeline work where nitrogen purging can displace oxygen rapidly, and for any operation where the potential for rapid oxygen depletion to severely low levels is a realistic hazard scenario. A sensor that has only been verified at 19% oxygen may respond correctly at the alarm threshold but has not been confirmed to read accurately through the full low-oxygen range below it.
Balance Nitrogen — Chemically Inert Carrier Gas
Nitrogen balance gas is chemically inert and does not react with any of the four active gas components in the mixture. This ensures concentration stability across the full shelf life of the cylinder and prevents any cross-interference between components during the calibration event. The non-reactive nature of nitrogen also means the cylinder contents are non-flammable at supply concentrations, keeping storage and transport straightforward under standard compressed gas handling procedures.
Five Cylinder Size Options — 34L to 116L
The cylinder is available in five sizes: 34L, 58L, 103L, 110L, and 116 litres. Smaller cylinders suit vessels, field teams, or worksites running a limited number of detectors with moderate bump testing frequency. Larger 103L to 116L cylinders reduce cost per calibration event and extend the interval between cylinder replacements for high-volume operations running daily bump tests across a large instrument fleet. Matching cylinder size to operational scale is one of the simplest ways to manage calibration gas cost without compromising programme frequency or documentation quality.
Technical Specifications
Product Type: Four-Gas Certified Calibration Span Gas Mixture
Cylinder Sizes (C10): 34L / 58L / 103L / 110L / 116 Litres
Carbon Monoxide (CO): 50 ppm
Hydrogen Sulphide (H2S): 25 ppm
Methane (CH4): 2.5% Vol / 50% LEL
Oxygen (O2): 12% Vol
Balance Gas: Nitrogen (N2)
Benefits
Correct Methane calibration reference for natural gas and CH4-specified detector fleets. Instruments factory-calibrated to Methane require a CH4 span gas for valid calibration. Substituting a different combustible gas — Pentane or Iso-Butane — will produce a LEL calibration result that does not match the sensor’s design reference, which can mean an inaccurate LEL reading in the field. This cylinder provides the correct CH4 reference at 50% LEL, eliminating calibration error caused by using the wrong combustible gas reference.
More rigorous O2 sensor verification than standard 18–19% oxygen mixtures. Most general-purpose four-gas span gas cylinders include oxygen at 18–19% vol — just below the alarm threshold — which confirms the sensor triggers correctly at the deficiency action level. Calibrating at 12% vol confirms the sensor reads accurately through a much wider low-oxygen range, which is the relevant verification for operations where severe oxygen depletion is a realistic hazard scenario, not just mild deficiency.
Full four-sensor verification in a single calibration connection. All four sensor types — LEL, H2S, CO, and O2 — are verified simultaneously with one cylinder connection, reducing calibration time and procedural complexity compared to managing four separate single-gas cylinders. For teams where detector downtime for calibration needs to be minimised, a single four-gas calibration event is the operationally efficient approach.
Certified calibration gas supports compliant documentation. Bump test and calibration records referencing a certified span gas cylinder — with the mixture specification, lot number, and certificate of analysis — meet the documentation standards required by OSHA confined space programmes, ISM Code safety management systems, and oil and gas operator permit-to-work audit requirements. A calibration performed with an uncertified or incorrectly specified gas cannot be documented as compliant with these standards.
Cylinder size flexibility manages calibration gas cost at any operational scale. Five size options from 34L to 116L allow procurement teams to match cylinder capacity to detector fleet size and bump testing frequency, avoiding both mid-programme gas shortages and over-purchasing. Getting this right meaningfully reduces the effective cost per calibration event over a year’s programme.
Who It’s For
The Safety Manager at a Natural Gas Distribution or Utility Operation
Your team uses portable four-gas monitors calibrated to Methane — the correct reference for the natural gas environments your workers enter daily. Your instruments need to be bump tested before every confined space entry and calibrated on the manufacturer’s recommended schedule. You need a reliable supply of CH4-based four-gas span gas at the right concentrations, with certified documentation to support your safety management system records. This cylinder provides the Methane LEL reference, the CO and H2S verification, and the more demanding 12% O2 sensor check your programme requires.
The Chief Officer or Marine Safety Officer on a Gas Carrier or Vessel with Inert Gas Systems
Before every tank entry or enclosed space access, your detectors need to be bump tested and confirmed functional. On a vessel where inert gas systems or nitrogen purging can drive oxygen levels well below 19%, verifying the O2 sensor against a 12% calibration standard gives you greater confidence that the instrument will read and alarm correctly through the full range of oxygen depletion your crew might encounter. The CH4 LEL reference covers the combustible gas hazard in natural gas cargoes, and the H2S and CO channels are verified in the same calibration pass.
The HSE Officer Managing Confined Space Entry at a Petrochemical or Industrial Site
Your site’s permit-to-work system requires detector bump testing before every confined space entry, and your calibration programme needs to be documented and audit-ready for both internal safety audits and regulatory inspection. Your instruments are Methane-calibrated, your confined space inventory includes spaces with natural gas exposure risk, and you need a certified four-gas span gas mixture at the concentrations your detector manufacturer specifies. This cylinder is that mixture, in the cylinder size that suits your fleet count and calibration frequency.
Possible Applications
- Natural gas distribution and pipeline maintenance — Bump testing and calibration of Methane-calibrated four-gas monitors used by technicians working on gas mains, service connections, and metering infrastructure
- Marine enclosed space and cargo tank entry — Pre-entry detector calibration on vessels where inert gas systems create severely oxygen-depleted atmospheres in cargo tanks, void spaces, and pump rooms
- Offshore platform confined space and hot work programmes — Calibration of portable four-gas monitors used for atmospheric monitoring during confined space entry and hot work permit execution on drilling and production platforms
- Upstream oil and gas production operations — Detector calibration for field workers on production sites where natural gas, H2S, CO, and oxygen depletion are simultaneous atmospheric hazards
- Petrochemical plant and refinery confined space entry — Calibration gas supply for four-gas monitors used by permit-to-work teams entering process vessels, storage tanks, and enclosed equipment in refinery and chemical plant environments
- Industrial utility confined space entry — Bump testing of four-gas monitors for workers entering sewers, pump stations, storage tanks, and enclosed process equipment where CH4, CO, H2S, and oxygen depletion are concurrent hazards
- Tunnel construction and underground infrastructure work — Detector calibration for enclosed underground environments where ground gas methane, CO from diesel equipment, and oxygen displacement are simultaneous hazards
- Power generation and energy sector confined space programmes — Calibration gas supply for multi-gas detectors used in boiler rooms, turbine enclosures, and underground cable vaults where CO, CH4, and oxygen depletion require simultaneous monitoring
Trust and Certifications
Certified Calibration Gas Mixture with Certificate of Analysis
Calibration gas cylinders used for instrument bump testing and calibration should be accompanied by a certificate of analysis (CoA) confirming the actual measured concentration of each component, the cylinder preparation date, the lot number, and the certified shelf life. The CoA provides the traceability required to confirm that calibration was performed with a gas mixture meeting the stated concentration specification — which is the foundation of a valid, defensible calibration record. For operations where calibration documentation is reviewed during OSHA inspections, ISM Code audits, or oil and gas operator HSE assessments, a certified calibration gas mixture is the correct standard.
Concentration Alignment with Methane-Calibrated Detector Manufacturer Specifications
The concentrations in this mixture — CO 50ppm, H2S 25ppm, CH4 2.5% / 50% LEL, O2 12% — are specified by detector manufacturers for four-gas instrument models factory-calibrated to Methane, including certain configurations of instruments from MSA, Industrial Scientific, Honeywell BW, and Draeger. Using the manufacturer-specified calibration gas concentrations ensures that calibration results are valid under the instrument’s design specification, supports warranty compliance where calibration records are required, and confirms sensor response against the correct chemical reference.
Supplied by Alright Engineering Solutions
This span gas cylinder is supplied by Alright Engineering Solutions Pte. Ltd., a Singapore-based distributor of portable and fixed gas detection equipment, certified calibration gas mixtures, regulators, and safety instrumentation. Alright Engineering Solutions serves the marine, oil and gas, petrochemical, utilities, and industrial safety sectors across Singapore and the wider regional market, providing span gas supply, instrument sales, calibration accessories, and technical support for gas detection and confined space entry programmes.
Accessories and Variants
Demand-Flow Regulator
A demand-flow regulator connects the span gas cylinder to the detector’s calibration inlet and delivers gas only when the instrument’s internal pump is actively drawing — preventing gas waste and ensuring accurate sensor exposure during bump testing and calibration. Alright Engineering Solutions can advise on the correct regulator specification for your cylinder valve type and instrument model.
Fixed-Flow Regulator
Fixed-flow regulators deliver calibration gas at a constant specified flow rate and are required for detector models that need a fixed-flow gas input during calibration. Available in multiple flow rate specifications to match different instrument calibration inlet requirements.
Calibration Tubing and Instrument-Specific Adapters
Silicone or PTFE calibration tubing and instrument-specific calibration cup adapters provide a secure, leak-free connection between the regulator output and the detector’s sensor inlet. A proper sealed connection prevents ambient air dilution of the calibration gas before it reaches the sensor, which would result in an inaccurate calibration reading and an unreliable calibration record.
Available Cylinder Size Variants
34 Litre (C10) — Compact cylinder for small teams, vessel use, or low-frequency calibration requirements
58 Litre (C10) — Mid-range option balancing portability and calibration capacity
103 Litre (C10) — Higher capacity for medium-sized detector fleets with regular bump testing programmes
110 Litre (C10) — Extended capacity for high-frequency daily calibration operations
116 Litre (C10) — Largest available size for high-volume calibration programmes and fleet-scale daily bump testing
Get in Touch
If you need to source the 4-MIX span gas cylinder — CO 50ppm, H2S 25ppm, CH4 2.5% / 50% LEL, O2 12%, Balance N2 — for your gas detection calibration programme, contact Alright Engineering Solutions to confirm cylinder size availability and request a formal quote.
Our team can also advise on compatible regulators, calibration accessories, and portable gas detection instruments to match your specific detector fleet and calibration programme requirements.
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