The type of sample tubing you use in conjunction with your gas monitor in remote sample applications and even during calibration can have a very pronounced effect on the gas readings that you obtain.
Not all sample tubing is created equal. Certain types of tubing will react with certain gases and therefore negatively impact the accuracy of the monitor readings in different ways.
For instance, silicone rubber tubing and other types of tubing that contains silicone should never be used with a gas monitor that has a catalytic bead combustible gas sensor. The silicone vapours that may be off-gassed from the tubing will react and quickly poison the sensor reducing its sensitivity and ability to accurately detect combustible gas.
PVC sample tubing, such as the flexible tubing the industry commonly refers to as Tygon tubing, may be suitable for sampling common gases such as oxygen, carbon monoxide, hydrogen sulphide and typical combustible gases that are measured at percent LEL levels, but PVC tubing can also react with many VOCs and other gases such as chlorine or ammonia and reduce the concentration of the gas that ultimately reaches the sensor in your gas monitor.
Polyurethane-based sample tubing may be more suitable for some reactive gases but may still be prone to attracting moisture in humid environments that will react with and reduce the sampled gas concentration.
My advice to anyone using a portable gas monitor, is to use sample tubing made of a high quality, non-reactive material for remote sampling and calibration in any application where gases of a highly reactive nature are being measured in low concentration. The most suitable sample tubing for reactive gas applications would be constructed of a Teflon (PTFE) based or Teflon-lined PVC material.
The type of sample tubing you use does and will make a difference. Keep it high quality and you will keep safe!
John: Very interesting article. A mistake so easily made and hard to detect unless you know. Thanks for the heads up.