Glossery

A printed certificate that shows a quantity of gas with a precisely specified mixture to conform to the stated mixing ratio.

Scale for measuring temperature that originated with Anders Celsius in the 1700s. Defined by the temperature at which water freezes (0

Upper limit of an employee

A sensor that contains two heated coils, connected by a Wheatstone bridge. One of the coils is treated with a catalyst to aid combustion. When a combustible gas passes through, the temperature increases at the catalyst-treated coil, changing the conductivity of that coil, causing a potential difference at the Wheatstone bridge. Measuring the change in potential difference enables the instrument to indicate the risk of explosion. A mesh filter is used to protect hazardous atmospheres from ignition. Gas has to permeate this mesh filter. Larger molecules have greater difficulty passing through the mesh filter, increasing the response time. Also, some gases burn hotter than others. LEL sensors are typically calibrated for methane, correction factors have to be applied for other gases.

A material that increases the rate of a chemical reaction while not being consumed by that reaction.

A highly toxic, flammable, colourless, odorless gas that is predominantly a product of incomplete combustion, and produced on a large scale as a precursor for the production of many other compounds. Carbon monoxide is detectable with colorimetric detection tubes and dedicated electrochemical cells. It is not detectable using a PID instrument. A carbon monoxide sensor is optional in almost all gas detectors with space for electrochemical sensors. Care should be taking with the carbon monoxide electrochemical sensor, as it is generally very cross-sensitive to most carbohydrates. An activated carbon filter is used to circumvent this cross-sensitivity, but that filter wears out even when not in use, by which time the instrument will report false-positives on carbon monoxide.

CO2 is a gas that occurs naturally in Earth's atmosphere. It is a product of the burning or corrosion of any carbonic compound. It is 60% heavier than dry air, making it an asphyxiant in confined spaces. It has a distinct odour that is only apparent at hazardous concentrations of over 3.9% by volume. CO2 is absorbed by plants to form carbohydrates through photosynthesis, releasing oxygen into the atmosphere. It is one of the greenhouse gases. CO2, although not toxic per se, is still considered a hazardous substance because of its propensity to replace ambient air, lowering oxygen levels. Lower oxygen levels are associated with concentration problems, headaches and general feelings of discomfort, even at concentrations below 1% by volume. This makes it important to monitor CO2 levels in places where people gather in poorly ventilated rooms, such as class rooms. CO2 is measurable through colorimetric detection tubes and specialized infrared sensors. Special models for class room use exist to alert occupants of the need to ventilate the room.

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A quantity of gas that is designed to calibrate a gas detector instrument. Calibration gas contains a precise and guaranteed concentration of one or more compounds. There are instruments to automatically calibrate one or more gas detectors, registering every bump test and calibration action to rigorously monitor the state of the gas detection equipment in use.

A procedure to ensure that a gas detection instrument responds correctly to gas hazards.

A quantity of gas that is designed to quickly test the functioning of a gas detector instrument by triggering all of its alarm thresholds, eg., air containing less than 18 Vol.% of oxygen, 2.5% of Methane, 200 ppm of carbon monoxide and 40 ppm of hydrogen sulfide. In most situations, standard calibration gas mixtures are used, although bump testing allows for cheaper and less precisely controlled mixtures. There are instruments to automatically bump test one or more gas detectors, registering every bump test and calibration action to rigorously monitor the state of the gas detection equipment in use.

Any gas that has a tendency to replace the air in a given environment, presenting a choking hazard more than a poisoning hazard.

A term for a gas detection instrument or accessory to signify that it meets criteria regarding (intrinsic) safety or appropriateness. Examples are: ATEX, UL&cUL, EMI/RFI, Marine Equipment Directive ("Wheel Mark") and many others, mostly according to local laws and regulations.

A colourless alkaline gas with a characteristic pungent smell. Ammonia is an important substance in agricultural, pharmaceutical and industrial cleaning environments. It is considered a hazardous substance because of its toxicity at low concentrations and prolongued exposure to even low concentrations should be prevented. Ammonia is measurable with a wide range of colorimetric detection tubes, electrochemical sensors (only suitable for low concentrations: at high concentrations, the expensive ammonia sensor is depleted quickly) and even with PID instruments (suitable and more cost effective at high concentrations as PID sensors are not depleted and are unharmed even in high concentrations of ammonia. This, and their quicker response time, makes PID instruments suitable for ammonia leak detection).

A term for air normally found in the environment, roughly 20.9% oxygen, 78% nitrogen and 1.1% other compounds (argon, carbon dioxide and trace gases), excluding water vapour (the concentration of which varies by location, altitude, temperature, weather and which is normally constant enough to be disregarded for gas detection purposes). In gas detection, ambient air is used to give instruments their zero calibration or fresh air calibration, provided they are free of contaminants.

An instrument to analyse breath alcohol, giving an indication of intoxication by alcohol consumption, especially in companies or environments with strict policies regarding alcohol intoxication. Also known coloquially as breathalyser.

The concentration of a specific gas at which an alarm is triggered.

A gas detector designed to serve only as an alarm in case of danger; does not provide real time concentration values. Alarm only instruments are normally disposable single gas detection devices, coloquially known as "beepers".

A precision instruments to measure air speed. They are frequently used to analyse air circulation and draught, and can also be used to predict propagation of hazardous chemicals in environmental incidents.