Gas Calibration Service

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Many buildings in New Zealand have some kind of fixed toxic gas monitoring system or could benefit from one.

We’ve listed the main areas where you may need to monitor for toxic gases:


Carbon Monoxide (CO) is a colourless odourless gas produced by combustion engines. When inhaled the CO can bind with the haemoglobin in the blood. In high concentrations it can stop oxygen binding to the blood therefore you suffocate. Low levels of CO can also build up over time having a similar effect to high levels for short periods. Carbon Monoxide exposure resulted in 379 deaths from 2006 to 2014 in NZ.

Nitrogen Dioxide (NO2) is one of a group of highly reactive gases known as oxides of nitrogen or nitrogen oxides (NOx). NO2 primarily gets in the air from the burning of fuel. Exposure to low levels of NO2 50-100ppm for 30mins can cause Bronciolitis and focal pneumonia with spontaneous recovery. Between 150-200ppm for 30mins can cause Bronchoiolitis fibrosa obliterans with death in 3-5 weeks. High exposure to NO2 >500ppm for 30mins, death within 2 days.

CO, NO2 control systems, where installed, help reduce the running of extract fans and ensure compliance with AS/NZ 1668.2. This is achieved by monitoring the concentration of CO and or NO2 and running the extract fans only when the time weighted average exceeds around CO 25ppm and NO2 1ppm (the International Mechanical Code recommended setpoint).

These systems significantly reduce the running costs as they only operate the fans during high traffic times. In some cases an alarm system consisting of a sounder / flasher may be in operation and this is typically enabled at between CO 50ppm OSHA maximum allowable concentration for a worker in continuous exposure in any 8 hour period say in a loading dock, or higher up to CO 100ppm in a short term car park.

These systems require at least annual calibration testing by comparing the sensors zero and span, against certified calibration gases as specified by the manufacturer. A bump test may be performed more regularly to check operation of the system, however span adjustment must be performed at least once a year [or more frequently if the sensors are getting older] by a competent person.

We are often asked how long a sensor should last. This is not simple to answer as the sensor life depends on the concentration of gas it is exposed to. Higher levels will deteriorate its accuracy faster. If exposed to lower levels it may last a long time. The manufacturers suggested life spans are typically based on a worst case and therefore if regular calibrations are performed and the span is adjusted based on the manufacturers recommendations the life of the sensor may be significantly extended without a loss of performance or safety thus saving the client lots of money over the life of the equipment.

There are many brands of CO / NO2 sensors installed in NZ including MSR, VCP, Honeywell, Critical Environment Technologies, ACI & others. Setpoint are able to support or calibrate all these brands.

Typical sites include Supermarkets, Council Apartment or Private vehicle car parks, Kiwirail, Mainfreight, Courierpost, Fonterra loading Bays, Bunnings, Mitre 10, Placemakers Trade drive throughs.


The sensors may be used for life safety such as oxygen depletion in a PC2 lab at a university, or in a storage area where liquid nitrogen or CO2 bottles are stored. Many labs or student learning areas, are reticulated with CO2 or Nitrogen. If these systems leak and oxygen is forced out of the space the alarm will be triggered at 18%. Normal safe oxygen level is 20.9%.

In this case the sensor does tend to have a fixed life span as the electrochemical sensor is always exposed to oxygen. A bump test needs to be performed every 6 months using a bottle of calibration gas (typically 18%) to confirm the correct operation of the life safety equipment lamps / sounders. Often these systems are integrated into a site wide Building Management System (BMS).

Other gases monitored in these facilities include VOC for formaldehyde, Hydrogen, CO2 or other gasses. Sometimes the sensors are located in an explosive area therefore an explosion proof housing may be required.


Many boiler rooms -especially older ones, may have a Natural Gas / LPG leak detection system. They generally have an atmospheric boiler, or a gas fired AHU. The sensor / controllers generally have two relay settings. The first at 10% LEL (lower explosion limit). This will typically be wired via interposing relays to close a shut off solenoid valve to isolate the gas system. The fire relay should also have the same effect. The boiler and other gas driven equipment will shut down. The second relay is triggered at 20% LEL This typically enables a sounder / flasher to warn it has detected a leak. The whole system needs to be checked it operates correctly and the boiler / shut off valve needs to be reset and checked it is running correctly.


Many commercial offices have large VRF systems. If a leak in these systems occurs in a small room a large quantity of refrigerant which is denser than air will sink and possibly displace the oxygen in the room. As refrigerant gasses are colourless and odourless it is possible to be asphyxiated. A local alarm will first act as a warning that refrigerant is present and the room should be evacuated and secondly to notify the Service Provider that the VRF system has a leak and requires repair.

A similar system is also used in plantrooms with centralised chillers. Refrigerant gas is becoming very expensive to purchase so early detection of a leak is very important.


Many supermarkets now use CO2 under very high pressure (over 40 bar) in large quantities within the Supermarket aisles, Plantrooms and chillers. All of these systems are required to have CO2 monitoring as part of the refrigeration system. These system MUST be tested and calibrated on a regular basis as part of the BWOF, however we believe this is not a common practice.


High concentrations of CO2 can be produced as part of the brewing process. CO2 in high concentrations have health consequences. These systems should be tested at least annually.


Setpoint staff have over 20 years of experience designing, programming, commissioning and calibrating these systems. It is not enough to just test the sensor and then walk away. The operation of the whole system from the sensor to the controller, to the VSD, lamps, sirens and fans needs to be tested, documented and verified. If the system is not operating as required Setpoint is able to provide a quotation to fix the existing system or if this is not economic, to replace it.

Please feel free to contact Setpoint if you have any of these systems or even one we have not come across yet.