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Links/Glossary – flammable gas detection, toxic gas detection and flame detection

Important terms / Glossary

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Auto-ignition temperature (AIT) of flammable gases and vapours. For non-flammable substances this column shows "n.a.". If known, the explosion group with subgroup, IIA, IIB or IIC (acc. to standard EN 60079-0), is listed in the 2nd line. If the ignition temperature is known, the 3rd line contains the temperature class. Electrical devices to be operated in hazardous atmospheres containing the considered flammable substance must at least be marked with the given explosion group and temperature class:

Allyl alcohol: AIT = 375 °C, IIB T2.

An electrical device must at least be marked IIB T2. Devices marked IIA T2 or IIB T1 are not allowed to be used in atmospheres where Allyl alcohol is present in potentially explosive concentrations.
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ATEX - What is ATEX? ATEX is the name commonly given to the two European Directives for controlling explosive atmospheres:

Directive 99/92/EC (also known as 'ATEX 137' or the 'ATEX Workplace Directive') on minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. The text of the Directive and the supporting EU produced guidelines are available on the EU-website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the information in the section on Equipment and protective systems intended for use in explosive atmospheres.

Directive 94/9/EC (also known as 'ATEX 95' or 'the ATEX Equipment Directive') on the approximation of the laws of Members States concerning equipment and protective systems intended for use in potentially explosive atmospheres. The text of the Directive and EU produced supporting guidelines are available on the EU website. For more information on how the requirements of the Directive have been put into effect in Great Britain see the section on Selection of equipment and protective systems.
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Boil. °C
This column is self-explaining, it shows the boiling point of the substance in °C (at 1013 hPa).

Below the boiling point given in °C the boiling point is printed in °F. This value is marked by a subsequent "°F".
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CE - CE marking is a declaration by the manufacturer that the product meets all the appropriate provisions of the relevant legislation implementing certain European Directives. CE marking gives companies easier access into the European market to sell their products without adaptation or rechecking. The letters CE stand for "Conformité Européenne" which means "European Conformity". They are a declaration by the manufacturer that his product meets the requirements of the applicable European Directive(s). For more information please visit
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CAS-Number - The CAS-number is a worldwide used code to identify a chemical substance unambiguously. This number is issued by the Chemical Abstracts Service and is the easiest way to characterize a chemical substance. Knowing the CAS-No. means to be able to get comprehensive information and links from internet and search engines. With the CAS-No. the considered substance is unambiguously specified.
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CSA - CSA stands for Canadian Standards Association, it means that the product has been tested and meets applicable standards for safety and/or performance, including the applicable standards written or administered by the American National Standards Institute (ANSI), Underwriters Laboratories (UL), Canadian Standards Association (CSA), National Sanitation Foundation (NSF), and others. For more information please visit
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Declarations Of Conformity - this links to CE Marking - A declaration of this nature means that the person responsible (normally a Technical Director) confirms that the products which are CE marked are actually certified. For more information please visit
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Dens. g/ml
The density ρ of the liquid in g/ml (= g/cm3) at 20 °C is listed. This value exists only for liquids, so gases are indicated by "Gas".
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Flpt. °C
Fashpoint of flammable liquids. Flammable gases do not have a flashpoint and are marked by "Gas". Gases or liquids being non-flammable are marked by 'n.a.'.

The flashpoint is defined as the temperature of a flammable liquid which (in a closed containment) is needed to obtain an ignitable vapour concentration above the liquid's surface. If environmental temperature and liquid temperature are clearly below the flashpoint (e.g. 10 °C lower), the liquid cannot be ignited.

Example: n-Nonane, flashpoint 31 °C, is not ignitable at 20 °C.

The relatively high flashpoint of n-Nonane is arising from its low vapour pressure. As already shown it is not possible to produce vapours of 100 %LEL under normal conditions (20 °C).

As the flashpoint is a temperature you can also convert a flashpoint F given in degrees Celsius into a flashpoint F given in degrees Fahrenheit using the conversion
flashpoint F given in degrees Fahrenheit

Example: n-Nonane, flashpoint is 31 °C,
flashpoint is 31 °C

Below the flashpoint F given in °C the flashpoint is printed in °F. This value is marked by a subsequent "°F".
Example: n-Nonane, flashpoint 88 °F
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Germ.: Source: Brandes, Möller (PTB): Safety Characteristic Data, Vol. 1: Flammable Liquids and Gases, Wirtschaftsverlag NW, 2nd Edition, 2008

If no data of LEL available, chemical catalogues or material safety data sheets have been consulted.
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IEC: Source: IEC 60079-20-1: 2010 "Explosive atmospheres -Material characteristics for gas and vapour classification"
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IECEx - Stands for International Electrotechnical Commissioning System for Certification to Standards relating to Equipment for use in Explosive Atmospheres. For more information on IECEx please visit:
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Important Remarks
Here you will find remarks concerning sensor poisoning by corrosive or polymerizing influences for catalytic sensors as well as information about response times (t20, t50).
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Leak detection?
A leak is an unpredictable abnormal release of gases or vapours of higher concentrations.

A leak has to be regarded as an exceptional event of a relative short duration.

In case of normal operation there is only clean air (without even low concentrations of the target gas or vapour).

A gas detection system for leak detection is not to measure a gas concentration but to give alarm reliably if a preset alarm threshold is exceeded.

That is why for leak detection rather the t20 or t50 response times are relevant instead of the t90-time. The given measuring ranges marked by "L" or "(L)" have to be interpreted as a range where an alarm threshold of the control unit can be set (choose e.g. 20% or 40% of full scale deflections).

After a gas release a leak gas detection system needs to be checked for proper function.
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Lwer explosion limit in %v/v. Non-inflammable gases and liquids are marked by 'n.a.'. If there is a void field this indicates that the LEL is unknown. Three values - if available - are listed here:
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Molw. g/mol
In the first line the molecular weight (mol weight) M is listed. The mol weight is used in many calculations, e.g. you can calculate the relative density of a gas or vapour by dividing value M by 28.96. If the result is less than 1 the gas is lighter than air. In most cases the result will be greater than 1 -so it is heavier than air. In case of vapours, however, the maximum vapour pressure (the maximum concentration at a given temperature) in an air/vapour mixture has to be regarded (see vapour pressure column 7): Vapours can never exist in a 100 %v/v-concentration!

Below the mol weight the value of the relative density compared to air is listed. It is marked by a subsequent "r" (for relative).

Example: n-Butanol: 2.56 r

Vapours of n-Butanol are 2.56 times heavier than air.

By using the mol weight M you can convert concentrations given in %v/v (= % by vol.) or ppm to obtain g/m3 or mg/m3.

Using the mol weight M you can also calculate the density of a gas in kg/m3 (at 20 °C and 1013 hPa) by simply multiplying with a factor of 0.04179:

Example: The mol weight of Propane is 44.1 g/mol, so the density of Propane is:

ρ = 0.04179 . 44.1 = 1.843 kg/m3

If density ρ and mol weight M are known you are able to calculate the amount of liquid to be evaporated in a given volume to obtain a defined vapour concentration. However, it is very important that this liquid is evaporated completely. This requires a sufficiently high vapour pressure.

Use the "calibration chamber formula": To obtain a vapour concentration c in a volume of 3 litres at 20 °C and 1013 hPa you have to insert the following amount F (in microlitres) of the liquid:
F of the liquid

Example: Ethyl acetate, M = 88.1 g/mol, ρ = 0.90 g/ml, LEL = 2.0 %v/v.

To obtain 50 %LEL (c = 1.0 %v/v) vapour of Ethyl acetate in the 3-litres-calibration chamber insert
50 %LEL (c = 1.0 %v/v)
of liquid Ethyl acetate.

If the flashpoint of the liquid is less than 25 °C the value of the amount to be inserted into the 3 litres calibration chamber to obtain 50 %LEL is printed below the value of the density. It is marked by a subsequent "v" (for volume).

Example: n-Hexane: 81 v

You need to insert 81 microliters into the Dräger Calibration Chamber to obtain 50% LEL of hexane vapour.
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Measuring performance
If the considered substance is subject of a measuring performance certificate ("measuring function for explosion protection") this is indicated by "Performance Approval".

Furthermore there are remarks like e.g. "detectability expected" or "on request". The relative sensitivities S in respect to the target gas might be of special interest.

For electrochemical sensors the given relative sensitivities S are only valid for new sensors and the values might fluctuate about < ± 30 %. An "L" in parenthesis indicates that this sensor is only suitable to be used for leak detection.

Example: OV1-sensor for Butylene oxide: "S = 0.4 (L)" means the sensitivity of the OV1-sensor exposed to Butylene oxide is 40 % compared to ethylene oxide. For Butylene oxide this sensor should only be used for leak detection purposes.

p20 mbar
Vapour pressure p20 of a liquid at 20 °C given in mbar (= hPa). Vapour pressure is only defined for liquids. So for gases instead of the vapour pressure you will find the marking "Gas" in this gas list.

The vapour of each liquid forms a pressure which depends on the nature of liquid and the liquid's temperature. If the vapour pressure is low, the liquid evaporates slowly and thus only produces low vapour concentrations (for such flammable liquids the flashpoint is usually high). The maximum vapour concentration cmax (called saturated vapour concentration), which can form in closed containments, can be calculated by dividing the given vapour pressure by the environmental atmospheric pressure.

Example: n-Nonane, p20 = 5 mbar, so
p20 = 5 mbar

So at 20 °C no vapour concentrations higher than 4900 ppm n-Nonane can exist. Only higher temperatures may produce higher vapour concentrations. Since the Lower Explosion Limit is 0.7 %v/v even in a closed containment at 20 °C no explosive vapour/air-mixtures of n-Nonane can form. It is essential that the "calibration chamber formula" does not apply for substances with a low vapour pressure, e.g. dosing to obtain 0.6 %v/v of n-Nonane vapour at 20 °C is not possible.
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SIL - Safety Integrity Level - is defined as a relative level of risk-reduction provided by a safety function, or to specify a target level of risk reduction. In simple terms, SIL is a measurement of performance required for a Safety Instrumented Function (SIF).

The requirements for a given SIL are not consistent among all of the functional safety standards. In the European Functional Safety standards based on the IEC 61508 standard four SILs are defined, with SIL 4 being the most dependable and SIL 1 being the least. A SIL is determined based on a number of quantitative factors in combination with qualitative factors such as development process and safety life cycle management. For more information please visit
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TLV Germ.: Source: TRGS 900, Edition February 2010. Source: NIOSH (Pocket guide to chemical hazards, US department of health and human services, 2005).

Commonly the TLVs are average values, but sometimes ceiling values (marked by a "c") are listed. In no case ceiling values are allowed to be exceeded.

If neither the TLV Germ. nor the TLV USA is listed this does not necessarily mean that the considered substance is not toxic. Short-term limit values have not been regarded in this gas list.

By means of the mol weight (column 4) you can convert the TLV to mg/m3 by multiplying the TLV given in ppm with the mol weight M and dividing it by 24. This conversion is valid for 20 °C.

Example: n-Nonane, M = 128.3 g/mol, TLV = 200 ppm:
n-Nonane, M = 128.3 g/mol, TLV = 200 ppm

The TLV is 1069 mg/m3.

Vice versa:
The TLV is 1069 mg/m3. Vice versa

Below the TLVs given in ppm the corresponding values given in mg/m3 are listed. They are enclosed in parenthesis. As these figures are exactly calculated they may slightly be different from officially issued values which are frequently rounded.
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TLV Germ. and TLV USA
Toxic limits as threshold limit values (TLV) or workplace limit values (WPL) in ppm.
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UL - The UL Mark on a product means that UL has tested and evaluated representative samples of that product and determined that they meet UL requirements. Under a variety of programs products are periodically checked by UL at the manufacturing facility to make sure they continue to meet UL requirements. The UL Marks may be only used on or in connection with products certified by UL and under the terms of written agreement with UL. In addition to these marks, UL also provides access to the marks required in a number of other key world markets. For more information please visit -
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USA : Source: mainly NIOSH (Pocket guide to chemical hazards, US department of health and human services, 2005).

These LELs occasionally deviate from the mentioned ones because the apparatus and procedures to determine the LEL are differently standardized in the USA.

By means of the mol weight (column 4) you can convert the LEL to g/m3 by multiplying the LEL given in %v/v with the mol weight M and dividing it by 2.4. This conversion is valid for 20 °C.

Example: n-Nonane, M = 128.3 g/mol, LEL = 0.7 %v/v, so
The LEL of n-Nonane is 37.4 g/m3.

And vice versa:
flashpoint is 31 °C

Below the LELs given in %v/v the corresponding values given in g/m3 are listed. They are enclosed in parenthesis.
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