Calibration FAQ

What Calibration Services do we Offer? 

We offer fast and simple gas calibration services.
Select if you have a single gas detector or multi-gas detector:

What is Calibration Gas?

Calibration gas is a certified gas mixture with precisely known concentrations used to adjust and verify gas detector accuracy. This procedure is called gas detector calibration. Calibration gas is manufactured to exacting NIST standards and comes with a Certificate of Analysis that validates its composition.

What is a Calibration Gas Bottle?

A calibration gas bottle is a pressurized cylinder containing precise concentrations of calibration gas mixtures. These bottles are specially designed with specific pressure ratings, valve types, and material compatibility to maintain gas stability. Calibration Gas Bottles are used as reference gas to calibrate gas detectors.

What is Gas Detector Calibration?

Gas detector calibration is the systematic process of adjusting a gas detector's sensors to respond accurately to known gas concentrations. This includes zeroing the instrument in clean air and adjusting the span using certified NIST calibration gas to ensure the detector accurately measures gas concentrations and alarm at appropriate levels.

  • Calibration procedures are highlighted in each product manual.
  • Forensics Detectors general gas calibration / bump testing procedures: click here.

What is Bump Testing?

  • Bump testing is a procedure where the user exposes the detector to a small amount “blast” of target gas to ensure the detector operates and alarms as programmed.
  • The function of this test is to verify proper operation and build user confidence, particularly in hazardous applications.
  • It is recommended to do a bump test when first purchased, followed by weekly tests.
  • We recommend daily bump testing (before use) when there is a risk of risk of injury, illness, or death from respiratory hazards such as oxygen deficiency and combustible or toxic gases. 
  • This recommendation is in line with the International Safety Equipment Association (ISEA) stating, "A bump test . . . or calibration check of portable gas monitors should be conducted before each day's use in accordance with the manufacturer's instructions." If an instrument fails a bump test or a calibration check, the operator should perform a full calibration on it before using it. If the instrument fails the full calibration, the employer should remove it from service. Contact the manufacturer for assistance or service.
  • Ozone bump testing is performed with a small ozone generator.
  • We do not offer bump gas for highly reactive gases such as ammonia, phosphine, nitrogen dioxide, and chlorine. In this case, we recommend purchasing 34 L calibration gas bottle to be used as bump gas.
  • Be aware of OSHA requirements regarding bump testing and calibration, see here.

What is the Difference Between Bump Gas and Calibration Gas?

While bump gas and calibration gas often use the same gas mixture, their purposes differ. Bump gas is used for daily functional tests to verify sensor response and alarm activation before using your gas detector. Calibration gas is used to precisely adjust sensor readings to match known reference gas concentrations. Both are critical for safety, but calibration provides actual adjustment, while bump testing verifies gas detector function.

How Often Must I Calibrate?

At least every 12 months. It may be warranted more frequently if you require the ultimate accuracy, are exposing the detector to extreme temperature and humidity conditions, sensor poisons, or exposure to high gas concentrations, which require more frequent calibration. Bump tests should be performed before each day's use.

What are the Different Names for Calibration Gas?

Calibration gas is known by several names in industry: cal gas, span gas (used during span calibration), test gas (for general verification), reference gas (as it provides a known reference point), standard gas (due to standardized concentration), and certified NIST calibration gas (emphasizing NIST traceability). 

How Do I Calibrate?

Calibration involves multiple steps: First, ensure the detector is in clean air and perform zero calibration. Then, attach the calibration cap and connect it to the regulator. Apply calibration gas at the manufacturer's specified flow rate (typically 0.5-1.0 L/min). Enter calibration mode on the detector and wait for readings to stabilize. Adjust readings to match the known concentration of calibration gas. Verify proper response and document the calibration. Always follow our specific instructions for your particular Forensics Detectors gas detector model.

What Equipment Do I Need to Calibrate?

Essential calibration equipment includes: certified calibration gas cylinder with proper concentration, compatible regulator with appropriate flow rate, calibration cap or cup specific to your detector model, connecting tubing (typically Silicone or Tygon), calibration documentation materials, and clean environment for zero calibration. Some systems may also require a docking station or automated calibration system.

What is a Calibration Gas Regulator?

A calibration gas regulator is a precision flow-control device that reduces the high pressure in the gas cylinder (often 1800+ PSI) to a safe, usable flow rate for calibration (typically 0.5-1.0 L/min). It includes pressure gauges, flow adjustment, and specific fittings for calibration gas cylinders. Different regulators are designed for different gas types and cylinder connections.

What is a Calibration Cap?

A calibration cap is a specialized fitting designed to deliver calibration gas directly to the sensor inlet at the correct flow rate. It's specifically designed for each detector model to ensure proper gas flow and concentration at the sensor, prevent ambient air dilution, and maintain consistent pressure. Some caps include multiple ports for different sensor configurations.

What is Zero Calibration?

Zero calibration is the process of setting the detector's baseline reading in clean, gas-free air. This establishes the "zero point" reference for all subsequent measurements. It should be performed in fresh air away from any potential gas sources, vehicle exhaust, or other contaminants. Some sensors may require special zero gas instead of ambient air.

What is Span Calibration?

Span calibration adjusts the detector's response to a known concentration of target gas, typically at 25-50% of the sensor's full scale. This process ensures the detector accurately measures gas concentrations throughout its range. It involves applying a precise concentration of calibration gas and adjusting the detector's reading to match the certified concentration.

Shall I Calibrate Myself (DIY) or have the Unit Calibrated via a Service?

The decision depends on several factors: staff expertise, equipment availability, and regulatory requirements. Professional calibration services offer certified technicians, proper equipment, and documentation, ensuring compliance and reliability. Self-calibration requires trained personnel, proper equipment, and thorough understanding of procedures. Many organizations use a combination, with routine calibrations done in-house and periodic professional verification.

When and Why Shall I Calibrate More Often?

More frequent calibration is necessary for several situations: exposure to sensor poisons or inhibitors, extreme temperatures or humidity, high gas concentrations, physical impacts or vibration, failed bump tests, erratic readings, critical safety applications, and regulatory requirements. Industries with highly toxic gases or LEL monitoring often require more frequent calibration schedules.

How Long Does Calibration Gas Last?

Calibration gas typically has a shelf life of 12-24 months from the manufacture date, depending on the gas mixture and cylinder type. Reactive gases may have shorter shelf lives. Factors affecting longevity include storage conditions, gas mixture stability, cylinder material compatibility, and initial pressure. Always check the expiration date on the cylinder and certificate of analysis.

How is Ozone Calibrated?

Due to ozone's instability and reactivity, cylinder-based calibration gas isn't practical. Instead, UV-generated ozone calibrators are used, which produce precise ozone concentrations on-demand through UV photometry. These systems create ozone by converting oxygen molecules using ultraviolet light, providing accurate, traceable calibration standards.

  • Only a few laboratories in the USA have the expensive, NIST calibrated equipment necessary to perform ozone gas detector calibration. 
  • Our ozone NIST traceability procedure is highlighted here.
  • The same considerations apply to ozone bump testing. Ozone bump testing must be performed with a small ozone generator.  

Does OSHA Require Gas Detector Calibration?

Yes, OSHA requires regular gas detector calibration under several standards including 1910.146 (confined spaces) and 1910.120 (HAZWOPER). While OSHA doesn't specify exact calibration intervals, they require following manufacturer's instructions and documenting all calibrations. They emphasize that proper calibration is essential for worker safety and require employers to maintain records of calibration procedures and results.

What is a Certificate Of Analysis?

A certificate of analysis (COA) is an official document provided with calibration gas that certifies its exact composition, traceability to NIST standards, uncertainty measurements, and shelf life. It includes: manufacturing date, expiration date, cylinder number, mixture composition, analytical method used, accuracy specifications, and stability information. This document is crucial for regulatory compliance and quality assurance.

Is Gas Calibration Required?

Yes, gas calibration is legally required in most jurisdictions and industries. Requirements come from multiple sources: regulatory agencies (OSHA, MSHA), insurance providers, industry standards (ISO, ANSI), manufacturer specifications, and workplace safety programs. Failure to calibrate can result in regulatory violations, invalidated warranties, and compromised safety.

What is the Best Way to Store Calibration Gas Cylinders?

Proper storage requires: temperature-controlled environment (10-30°C/50-86°F), dry location away from direct sunlight, secure upright position with chains or straps, valve protection in place, segregation by gas type, good ventilation, clear hazard labeling, inventory tracking system, and away from corrosive atmospheres. Cylinders should be easily accessible but protected from damage.

How Do We Ensure Gas Calibration Cylinder Safety?

Gas cylinder safety involves multiple measures: proper training for handlers, secured storage in upright position, valve protection caps when not in use, proper transportation methods, regular inspection for damage, clear labeling and identification, separation of incompatible gases, proper ventilation, use of appropriate regulators, leak testing connections, and emergency response procedures.

What Are The Common Causes For Gas Detector Calibration Failure?

Common calibration failures include: expired or degraded calibration gas, contaminated or damaged sensors, incorrect flow rates, blocked filters or sampling lines, electromagnetic interference, extreme temperature or humidity, incorrect calibration procedure, depleted sensor life, interference gases present, improper zero calibration, and faulty regulators or connections.

How do you know when it is time to calibrate?

Calibration timing is indicated by: manufacturer's recommended intervals, failed bump tests, erratic or slow readings, exposure to high gas concentrations, sensor poisons or inhibitors, physical impacts, environmental extremes, regulatory requirements, incident investigations, and maintenance schedules. Many modern detectors also have calibration due reminders.

How Do You Know if a Successful Calibration Was Undertaken?

Once calibrated it is prudent to undertake a verification step to confirm successful calibration. This means confirming your zero baseline (fresh air) and span calibration by exposing the gas detector to your calibration gas and verifying repeatability to the calibration reference gas level used. 

What Should Be Documented When Calibrating?

Calibration documentation should include date and time, detector identification and serial number, sensor type, calibration gas concentrations and lot numbers, certificate of analysis reference, zero readings, span readings, pass/fail status, environmental conditions, technician name and certification, pre and post results, and next calibration due date.

How Does Temperature and Humidity Affect Gas Detector Calibration?

Temperature and humidity significantly impact gas detector calibration through multiple mechanisms: sensor sensitivity changes with temperature, condensation can block sensor ports, humidity affects gas concentration calculations, extreme temperatures can damage sensors, response times vary with temperature, and sensor baselines drift with environmental changes. Manufacturers specify operating ranges and correction factors. Calibration should be performed at similar conditions to operational use.

What are the Signs of a Gas Detector Requiring calibration?

Key indicators include: slow response to gas exposure, erratic or unstable readings, failed bump tests, zero drift in clean air, inconsistent alarm activation, unusual sensitivity to interference gases, exposure to extreme conditions or contaminants, physical impacts or drops, error messages on display, and exceeding calibration interval. Regular inspection can identify these signs early.

How long does a typical calibration take?

A typical calibration process takes 3-8 minutes per sensor, with total time varying based on detector type and number of sensors. This includes: warm-up time (2-3 minutes), zero calibration (1-2 minutes), span calibration (2-3 minutes per gas), and system verification. 

Why is Calibration Gas Expensive?

Calibration gas cost reflects several factors: precise mixing technology requirements, specialized cylinder preparation, high-purity source gases, analytical certification process, NIST traceability, stability testing, limited production volumes, specialized handling and shipping requirements, short shelf life, and regulatory compliance costs. Custom mixtures and reactive gases typically cost more.

Is Calibration Gas Dangerous?

Yes, calibration gases can pose various hazards: toxicity, flammability, high pressure, asphyxiation risk, and reactivity. Many mixtures contain hazardous components at significant concentrations. Safe handling requires: proper training, ventilation, personal protective equipment, proper storage, leak detection, emergency procedures, and understanding of safety data sheets. Transportation is regulated under hazardous materials rules.

What is NIST and Why is it Important?

The National Institute of Standards and Technology (NIST) is the U.S. authority for measurement standards. For gas calibration, NIST provides reference materials and standards ensuring measurement accuracy and consistency. NIST-traceable calibration gases have documented unbroken chains of comparisons to NIST standards, ensuring reliability and legal defensibility of measurements. This traceability is crucial for regulatory compliance and quality systems.

How do I dispose of my calibration gas cylinder?

Proper disposal involves: checking with supplier for return programs, never venting toxic or flammable gases, using appropriate cylinder depressurization methods, following local regulations, documenting disposal, maintaining chain of custody, and using licensed hazardous waste handlers when required. Many suppliers offer cylinder return and recycling programs. Empty cylinders must still be handled as hazardous materials.

Where Shall I Calibrate?

Calibration should be performed in a controlled environment with: adequate ventilation, stable temperature (15-25°C), low humidity, away from strong electromagnetic fields, no interfering gases present, protection from wind and weather, proper lighting, clean air source for zero calibration, enough space for equipment setup, and appropriate safety equipment nearby. Indoor locations should have ventilation systems capable of handling potential gas releases.

What are Calibration Gas Equivalency Factors?

Calibration gas equivalency factors are mathematical constants used to relate sensor responses between different gases. These gases are sometimes called surrogate gases. They allow calibration with one gas while measuring another based on known cross-sensitivities. 

Why is there a lead time of 2 weeks on calibration gas cylinders?

The two-week lead time encompasses several necessary steps: custom gas mixture preparation, stabilization period for mixture equilibrium, multiple analytical tests for concentration verification, NIST-traceable certification process, quality control checks, certificate of analysis generation, cylinder preparation and treatment, safety checks, packaging for shipment, and transportation arrangement. Special mixtures or reactive gases may require longer lead times.

How do you choose the right concentration of calibration gas?

Selection criteria includes: typical workplace exposure levels (usually 25-50% of full scale), regulatory requirements, alarm setpoints, sensor range and resolution, manufacturer recommendations, measurement accuracy requirements, and application-specific needs. The concentration should be high enough to verify proper response but below alarm levels when possible. Always use the manufacturer's recommended calibration gas and gas concentrations.

What is Cross-Sensitivity in Gas Calibration?

Cross-sensitivity occurs when a sensor responds to gases other than its target gas. This affects calibration by: requiring consideration of interference gases present, potentially necessitating correction factors, influencing choice of calibration gas mixtures, affecting measurement accuracy, and determining sensor placement. Understanding cross-sensitivity is crucial for proper calibration and accurate field measurements.

What is the difference between calibration gas and span gas?

While technically the same product, these terms reflect different uses. Calibration gas refers to the broader use of certified gas mixtures for all detector adjustments and verifications. Span gas specifically refers to the gas used for spanning (adjusting sensor gain/sensitivity). Both require precise certification and traceability, but the terms are often used interchangeably in industry.

What flow rate should be used for calibration gas?

Flow rates typically range from 0.5-1.0 L/min, but specific requirements depend on: sensor type, manufacturer specifications, calibration cap design, gas mixture composition, and environmental conditions. Too high flow can pressurize sensors, while too low flow allows ambient air dilution. Smart regulators often automatically provide the correct flow rate. Consistent flow is crucial for accurate calibration.

Can I use calibration gas from a different manufacturer?

Using alternative manufacturer's calibration gas is generally not recommended because: it may void warranty coverage, concentrations may not match specifications, cylinder fittings might be incompatible, traceability might not meet requirements, and sensor response may differ. If used, verify: compatibility with sensor, proper concentration range, acceptable accuracy, and appropriate certification.

What does "traceable calibration gas" mean?

Traceable calibration gas has documented, unbroken chain of comparisons to national standards (typically NIST). This includes: analytical measurements linking to primary standards, documented uncertainty calculations, calibration of all measurement equipment used, quality control procedures, and complete record keeping. Traceability ensures reliability and legal defensibility of subsequent measurements.

What safety data sheets are required for calibration gas?

Required safety documentation includes: Safety Data Sheets (SDS) for each component gas, DOT shipping documentation, certificates of analysis, cylinder labels with GHS information, emergency response information, handling procedures, exposure limits, hazard classifications, first aid measures, and disposal requirements. These must be readily available where gases are used or stored.

Why do some calibration gases require balance gas?

Balance gases (typically nitrogen or air) serve multiple purposes: maintaining stable total pressure, ensuring proper gas mixing, preventing chemical reactions between components, achieving precise concentrations of active components, improving shelf life, and ensuring consistent flow characteristics. The choice of balance gas can affect sensor response and measurement accuracy.

What is a multi-gas calibration mixture?

Multi-gas calibration mixtures combine several target gases in one cylinder to calibrate multiple sensors simultaneously. Benefits include: reduced calibration time, fewer cylinders to maintain, lower costs, simplified procedures, and consistent calibration conditions. However, they require careful composition design to ensure component compatibility, stability, and appropriate concentrations for all sensors being calibrated.