Choosing the Best Gas Detector - Intrinsic Safety and Ingress Protection

Choosing the Best Gas Detector

"Best" gas detector doesn't come from any one manufacturer; it’s the instrument that best fulfills the requirements for your monitoring program
Ways in which gas detectors are used can vary widely between different programs
The instrument that provides the best service and value for one program may not be the best choice for another

Classification for Intrinsic Safety

Intrinsically Safe devices prevent explosions in hazardous locations by employing electrical designs that eliminate the possibility of ignition
- Generally involves adding protective components in series with energy storage devices to reduce risk of ignition due to spark or increased surface temperature of components
- Design elements may also include flame arrestors or other components to locally contain an explosion in the event that there is ignition
- Combustible sensors contain an integral flame arrestor for this purpose
- Classification for Intrinsic Safety is based on performance of the instrument when tested in a specific flammable atmosphere

UL / CSA Product Markings

Typical North American Marking:
- c-CSA-us or c-UL-us Classified as to intrinsic safety for use in Class I, Division1 Groups A, B, C, and D, and Class II Groups E, F and G Hazardous Locations
  - Class I: A location where there is a danger of explosion due to the presence of a flammable gas or vapor
    - Under the North American system the hazardous gases are subdivided into Divisions. The IEC system divides it into Zones
  - Class II: A location where there is a danger of explosion due to the presence of a flammable dust

Class I Divisions vs. Zones

CEC/NEC Division Classification	IEC Zone Classification
Class I, Division 1: Ignitable concentrations can exist under normal operating conditions; may exist frequently because of repair, maintenance or leakage; or may exist due to breakdown of equipment in conjunction with an electrical failure	Class I, Zone 0: Where ignitable concentrations are present continuously or for long periods of time
	Class I, Zone 1: Where ignitable concentrations are likely to exist under normal operations; may exist frequently because of repair, maintenance or leakage; may exists due to breakdown of equipment in conjunction with an electrical failure; or adjacent to Class I, Zone 0 locations.
Class I, Division 2: Where volatile flammable liquids are stored, etc. in closed containers; where ignitable concentrations are normally prevented by positive pressure ventilation; or adjacent to Class I, Division 1 locations	Class I, Zone 2: Where ignitable concentrations are not likely to exist in normal operation or may exist for a short time only; where volatile flammable liquids are stored, etc. in closed containers; where ignitable concentrations are normally prevented by positive pressure ventilation; or adjacent to Class I, Zone 1 locations.

Classification for Intrinsic Safety

Hazardous Location Classifications
- Class I, Division 1, Groups A, B, C, D
- Class II, Groups E, F, G
Groups A,B,C and D are explosive gases and vapors
Groups E, F, and G are explosively combustible dusts

UL / CSA / NEC Combustible Gas Classification Groups

Class I, Division 1 Groups A, B, C, D

Group	Gas or Vapour	LEL (%)	UEL (%)
A	Acetylene	2.5	80.0
B	Hydrogen	4.0	5.0
C C C	Diethyl ether Ethylene H2S	1.9 3.1 4.3	48.0 32.0 45.0
D D D D D D	Ammonia Butane Gasoline Methane CO₂ Propane	15.0 1.9 1.4 5.3 12.5 2.2	28.0 8.5 7.6 15 74.2 9.5

European Cenelec / ATEX Product Markings

European Combustible Gas Classification Groups

Combustible gas categories divided into two groups:
- Group I for mines susceptible to methane
- Group II for explosive gases for locations other than mines; group II is divided into three sub groups:
  - IIA: Atmospheres containing propane or gases of an equivalent hazard
  - IIB: Atmospheres containing ethylene or gases of an equivalent hazard
  - IIC: Atmospheres containing hydrogen or gases of an equivalent hazard.

Temperature Codes

Substance	Temperature Classification	AIT (°C)
Methane	T1	595
Propane	T1	470
Ethylene	T2	425
Acetylene	T2	305
Hydrogen	T1	560

The auto-ignition temperature is the temperature, in °C, at which a gas will ignite spontaneously without another source of ignition
Temperature code groupings correspond to the range of autoignition temperatures in which a particular gas belongs

Temperature Codes

Temperature Class	Autoignition Temperature Limit for Gases Measured (°C)
T1	450
T2	300
T3	200
T4	135
T5	100
T6	85

Temperature code groups can also sbe expressed as a range of temperatures
Gases with low autoignition temperatures are the ones most easily ignited by increasing the temperature once the gas is present in LEL concentrations
- As an example: A T3 rating means that the instrument is only Classified as IS for gases with autoignition temperatures greater than 200 °C.
- The AIT for propane is 470 °C.
- Using an instrument with a T3 rating to monitor for the presence of propane would be well within the scope of its IS Classification.

CE Mark

"CE" stands for the French "Conformité Européene"
CE Marking on a product is the manufacturer's declaration that the product conforms with the relevant European health, safety and environmental "Product Directives"
Product Directives contain the essential requirements, performance levels, and "Harmonized Standards" for technical specifications to which the products must conform
CE Marking indicates to EEC governmental officials that the product may be legally placed on the market in their country
CE Marking includes declaration that the product conforms with EMC Directive 89/336/EEC whichm governs product susceptibility to RFI / EMI interference

ISO Registration

9001: 2000 Edition
Old edition allowed mediocre quality, as long as product produced consistently
New edition includes requirement for "continual product improvement"

Ingress Protection

Enclosure Rating Definitions for IEC (International Electrotechnical Commission)
The IEC enclosure rating always starts with the letters "IP" and ends in two numbers
The first number describes the degree of contact prevention and guarding against solid foreign objects
The second number describes the degree of water protection

First No.	Degrees of Contact Prevention and Guarding Against Foreign Objects
0	No protection of personnel from direct contact with active or moving parts. No protection from access of a solid foreign object.
1	Protection of personnel from accidental large area direct contact with active or internal moving parts but no guard against intentional access to such parts. Protection from access of solid foreign object larger than 50mm in diameter
2	Protection of personnel from finger contact with active or internal moving parts. Protection from access of solid foreign object larger than 12mm in diameter
3	Protection of personnel from touching active or internal moving parts with tools, wires or similar foreign objects thicker than 2.5mm.. Protection from access of solid foreign matter larger than 2.5mm in diameter.
4	Protection of personnel from touching active or internal moving parts with tools, wires or similar foreign objects thicker than 1mm.
5	Total protection of personnel from touching voltage carrying or internal moving parts. Protection from harmful deposit of dust. Access of dust is not completely prevented.
6	Total protection of personnel from touching voltage carrying or internal moving parts. Protection from access of dust.

2^nd No.	Protection	Details
0	Not protected	-
1	Dripping water	Dripping water (vertically falling drops) shall have no harmful effect.
2	Dripping water when tilted to 15°	Vertically dripping water shall have no harmful effect when enclosure tilted at an angle up to 15° from normal position.
3	Spraying water	Water falling as spray at any angle up to 60° from the vertical shall have no harmful effect
4	Splashing water	Water splashing against enclosure from any direction shall have no harmful effect.
5	Water jets	Water projected by a nozzle against enclosure from any direction shall have no harmful effects
6	Powerful water jets	Water projected in powerful jets against the enclosure from any direction shall have no harmful effects.
7	Immersion up to 1m	Ingress of water in harmful quantity shall not be possible when immersed under defined conditions of pressure and time (up to 1 m of submersion).
8	Immersion beyond 1m	Suitable for continuous immersion in water under conditions specified by the manufacturer.