Prevent Contamination Of Your Gas Mixtures

Many instrumentation manufacturers are producing gas detection monitors with multiple sensor capability of 4, 5, 6 or more sensors in one instrument. Many of those instruments are measuring toxic gases such as ammonia, chlorine, hydrogen cyanide, nitrogen dioxide and other gases.   

Calibration and bump testing will be a requirement for all these sensors but unlike a standard 4 gas mixture of H2S/CO/CH4/O2 each gas must be separate and cannot generally be mixed with other gases. There are potential issues which can arise if correct procedures for handling these gases is not used.

This creates a requirement for understanding the best practice in selecting materials and using correct procedures for accurate calibration and longevity of gas mixtures.

Here are a few BEST PRACTICE technical tips for all gas mixtures:

1. Always use Teflon or Teflon lined tygon tubing for mixtures containing corrosive/ reactive gases.

• • Gases such as ammonia, chlorine and nitrogen dioxide will adsorb onto standard tygon tubing. Even with a short length of tubing (60cm) a 10ppm CL2 mixture will be reduced to zero if using the incorrect tubing. Adsorption could have other implications in terms of reaction with other compounds used in the tubing. 
  • Use different tubing for each gas type to prevent further contamination
  • Use the shortest length of tubing which is practical to prevent moisture build up in the tubing and reduce loss of gas sample through the walls of the tubing

2. Always use stainless steel regulators for corrosive/reactive gas mixtures. 

• • Corrosive gases will eventually corrode nickel plated regulators exposing the brass base which can react with the gas mixture. This reaction could cause impurities to enter the gas cylinder and deteriorate the gas mixture causing it to break down. At a minimum the corrosion of nickel plated regulators could cause the regulator to fail leading to leaks and catastrophic failure of the valve seats.
  • Nickel Plated Brass regulators are fine for non-corrosive gases, H2S or SO2 (<50ppm)
  • Stainless steel regulators should be used for other gases.

3. Never use the same regulator with different gas mixtures.

• • Select your regulator material based upon the gas mixture and then label the regulator with the chemical symbol, so the regulator is only used with that gas type. ( H2S , NH3, CL2….) .  
  • Using the same regulator can cause cross contamination between the gases. 
  • Small amounts of gas can remain in the regulator. If you connect the regulator to a cylinder incorrectly the gas in the regulator could be drawn into the cylinder potentially contaminating the gas mixture.

4. Always put your cylinder onto your regulator the correct way.

• • Turn on your regulator. Hold the regulator with the gauge pointed away from you toward the ground. Screw the cylinder onto the regulator. Turn off the regulator until ready for use.
  • To remove. Turn on the regulator. Hold regulator as above and unscrew the cylinder from the regulator.

5. Never store your gas mixtures in a refrigerator or cold storage area.

• • Moisture is the death for all gas mixtures. 
  • If you store gas mixtures in a cold place condensation will occur when used in normal ambient temperatures. This moisture could be drawn into the cylinder when a regulator is put onto the cylinder incorrectly, resulting in the moisture breaking down the gas mixture.