Toxic gases

A toxic gas may be defined as a chemical compound that, when inhaled, ingested or absorbed through the skin provokes a wide range of damage, from minor irritations to death. It is possible to come in contact with these gases in different situations and, it is the employer’s liability to insure that no workers are exposed to concentrations exceeding the safe limits.

Exposure to toxic gases must be calculated on the Time WeightedAverage (TWA) basis, which is the medium concentration relevant to a common 8 hours working day, at which it is considered that all employee can be exposed without injuring their health.

Exposure limits to toxic gases have been established by occupational safety agencies and may vary according to local directives. They commonly refer to the short term exposure limit (STEL) defined by the American Conference of Governmental Industrial Hygienists (ACGIH). The lower is the STEL –either expressed in ppmor mg/m3 –the higher is the compound toxicity.

In the United Kingdom the normative reference is known as COSHH (Control of Substances Hazardous to Health) and its limits are published by HSE (Healthand Safety Executive) in the guide EH40. MEL(Maximum Exposure Levels) concerns the most dangerous compounds; an exposure to them should be the shortest possible and in any case no longer than these levels.OES(Occupational Exposure Standards) concerns less dangerous substances and the exposure can be considered sure if under these two limits:LTEL(Long Term Exposure Limit) exposure during 8 hours daily workSTEL(Short Term Exposure Limit) applicable to occasional exposures (15 minutes).

MAK (Maximale Arbeitsplatz Konzentration) is the system reference used in Germany and in some nearby countries. Its values are published by DFG and are based on experimental effects of toxic substances observed on people and animals. MAK value isdefined as the maximum tolerable concentration of a gas or of a toxic vaporin a working place, without impairing personnel health. Exposure for 8 hours a day for 5 days a week (40 hours) can be repeated for a long time without bad effects on people’s health.

In the USA Occupational Organizations are OSHA and NIOSH. As for most of the Countries, in the USA exposure limits are defined as TLV(Threshold Limit Value), STEL(Short Term Exposure Limit) and TWA (Time Weighted Average).

TLV: (threshold limit values), limit below which toxic substances in working places generally do not provoke negative health effects.

TLV -TWA: (time weighted average, MAK medium), allowable medium concentration time weighted on a 8 hour workday and 40 hour workweek at which it isconsidered that personnel may be exposed.

TLV -STEL: (Short Term Exposure Limit), maximum concentration for a continuous exposure for up to 15 minutes, on condition that the TLV is not exceeded.

TLV -C: (Ceiling), concentration ceiling, borderline concentration, value that cannot be exceeded not even for a second.

Toxic gas concentration in the air is expressed in parts per million (ppm), which is the gas concentration measure in volume. The alternative unit in Europe is milligram per cubic meter in the air (mg/m3), which is a mass measure. An approximate and suitable conversion from ppm to mg/m3 and vice versa, can be obtained by knowing the gas molecular weight at 25°C and at 1 bar atmospheric pressure. The relevant formula is:TLV (mg/m3) = TLV (ppm) * molecular weight (g) / 24.45

The detection of hazardous gases has always been a complex subject, making the selection of the appropriate sensor, instrument, or equipment a difficult task. Sigma offers electrochemical, catalytic, & non-dispersive infrared(NDIR) sensors for toxic and flammable gases.

 

Sigma offers a variety of options to cover most of your applications, some of which are listed hereunder

 

Sigma 95H series

 

Sigma 95H series wall mounted type of gas detector with alarm light, is monitoring gas concentration in different applications 24h continuously. Using high quality sensors, and advanced micro-process technology, with data display, high/low alarm, offers fast response, high precision and good stability.
Powered by 24V DC, with 4-20mA, RS485, relay signal output and Explosion proof, is suitable for different kinds of applications.

Features
Monitor the specific gas concentration in the environment and activates the alarm when it is over the set point.
With self-calibration and zero calibration function, it makes the detection more accurate and reliable.
With temperature compensation, it is able to function under conditions of different temperatures.
A two-stage alarm (High/Low) with sound and light, is user adjustable.
An Infrared controller can adjust remotely the alarm point settings, zero calibration, and address modification.
Can output one or two on-off signals, can drive ventilator or
solenoid valve and other external devices.
Working Voltage：12-36V DC
Housing：die-cast aluminum + stainless steel (alarm light)

Product advantages
Using high quality sensors.
Standard equipped with three-wire system 4-20mA analog output; relay output; RS485 output (optional)
Unique infrared non contact control
Compatible with all kinds of control alarms, PLC, DCS and
other control systems, can be remote monitored.
Explosion-proof design, fast, reliable and stable.
Explosion-proof grade: II 2G Ex db IIC T6 Gb IP65
With self-calibration function and three standard keys will be used for on-site maintenance.

 

Technical Specifications
Gas Detected: As ordered from a variety of different gases
Detection Principle: Infrared, Electrochemical, Catalytic
Measuring Range: depending on the application
Installation Method: Wall-mounted, piping type, flow-type(according to the detection application)
Output signal 4-20mA, RS485,  relays (optional)
Precision ≤±3%F.S. (higher precision is optional)
Zero shift ≤±1%（F.S./year）
Display 4 digits Nixie tube display.
Connection mode G1/2 external thread explosion-proof flexible pipe
Thread Size M45*2mm
Temperature –20℃～50℃
Humidity 0-95%RH (non-condensing)
Explosion-Proof Ex dⅡCT6
Degree of protection IP65
Alarm mode Sound, light
Material Case: Die-cast aluminum
Sensor housing: aluminum alloy or 316 stainless steel
Power 12-36V DC
Dimensions 180×150×90mm
Weight ≤1.6kg

 

Gases,

CO, H2S, O2, N2, NH3, CL2, H2, CH2O, O3, CO2, NO, NO2, SO2, ETO, PH3, HCL, HCN, COCL2, CLO2, SiH4, F2, HF, HBr, H2O2, B2H6, AsH3, GeH4, N2H4, THT, Br2, C2H2, C2H4, CH3OH, C2H5OH, CH4S, C8H8, C4H6, VOC/TVOC, CH3Br, C6H6, C7H8, C8H10. Other gases on request.

 

Applications

  • Petrochemical & Chemical Industry
  • Marine
  • Food & Pharmaceutical Industry
  • Electronics
  • Municipal Engineering & Utilities
  • Agricultural & Environmental Protection
  • Other Industries

 

The flammable gases

The simplest organic compounds are known with the name of Hydrocarbons (composed of Carbon and Hydrogen) and represent the major constituents of  the petrol gas.
Composed of an atom of Carbon and four atoms of Hydrogen, the Methane represents the simplest form of Hydrocarbons: it is the first element of Alkanes.
The first ten alkanes are:
CH4     Methane (gas)     C6H14   Hexane (liquid)
C2H6   Ethane (gas)        C7H16   Heptane(liquid)
C3H8   Propane (gas)      C8H18   Octane (liquid)
C4H10 Butane (gas)        C9H20   Nonane(liquid)
C5H12 Pentane (liquid)    C10H22 Decane(liquid)

Explosive limits
The Lower Explosive Limit (LEL) defines the lowest concentration of a combustible in air that allows the explosion. There could be a high explosion risk even with very small gas concentrations: in fact a great part of flammable gases and vapors have the LEL figure below 5% of volume.The Upper Explosive Limit (UEL) defines the maximum concentration of fuel in air that may causes explosion. Concentrations of the combustible above the UEL cannot generate explosion because of the insufficient concentration of the commenter (typically Oxygen).

 

Sigma 95H series

 

 

Sigma 95H series wall mounted type of gas detector with alarm light, is monitoring gas concentration in different applications 24h continuously. Using high quality sensors, and advanced micro-process technology, with data display, high/low alarm, offers fast response, high precision and good stability.
Powered by 24V DC, with 4-20mA, RS485, relay signal output and Explosion proof, is suitable for different kinds of applications.

 

Features
Monitor the specific gas concentration in the environment and activates the alarm when it is over the set point.
With self-calibration and zero calibration function, it makes the detection more accurate and reliable.
With temperature compensation, it is able to function under conditions of different temperatures.
A two-stage alarm (High/Low) with sound and light, is user adjustable.
An Infrared controller can adjust remotely the alarm point settings, zero calibration, and address modification.
Can output one or two on-off signals, can drive ventilator or
solenoid valve and other external devices.
Working Voltage：12-36V DC
Housing：die-cast aluminum + stainless steel (alarm light)

 

Product advantages
Using high quality sensors.
Standard equipped with three-wire system 4-20mA analog output; relay output; RS485 output (optional)
Unique infrared non contact control
Compatible with all kinds of control alarms, PLC, DCS and
other control systems, can be remote monitored.
Explosion-proof design, fast, reliable and stable.
Explosion-proof grade: II 2G Ex db IIC T6 Gb IP65
With self-calibration function and three standard keys will be used for on-site maintenance.

 

Technical Specifications
Gas Detected: As ordered from a variety of different gases
Detection Principle: Infrared for CO2, Electrochemical for others
Measuring Range: depending on the application
Installation Method: Wall-mounted, piping type, flow-type(according to the detection application)
Output signal 4-20mA, RS485,  relays (optional)
Precision ≤±3%F.S. (higher precision is optional)
Zero shift ≤±1%（F.S./year）
Display 4 digits Nixie tube display.
Connection mode G1/2 external thread explosion-proof flexible pipe
Thread Size M45*2mm
Temperature –20℃～50℃
Humidity 0-95%RH (non-condensing)
Explosion-Proof Ex dⅡCT6
Degree of protection IP65
Alarm mode Sound, light
Material Case: Die-cast aluminum
Sensor housing: aluminum alloy or 316 stainless steel
Power 12-36V DC
Dimensions 180×150×90mm
Weight ≤1.6kg

 

Applications

  • Petrochemical & Chemical Industry
  • Marine
  • Food & Pharmaceutical Industry
  • Electronics
  • Municipal Engineering & Utilities
  • Agricultural & Environmental Protection
  • Other Industries