Gas Detection Information

FAQ’s

What do the below abbreviations mean on my gas detector?
O2 – Oxygen
LEL – Combustible Gases
H2S – Hydrogen Sulfide
CO – Carbon Monoxide

What should be the normal readings on my gas detector in a clean atmosphere?
O2 – 20.9%
LEL – 0%
H2S – 0ppm
CO – 0ppm

When I turn my gas detector on the readings are different from that above. Why?
There are two possible reasons for this:
1. The sensors have fluctuated slightly (normally due to gas exposure or the unit being dropped).
2. The gas detector has been started in an unclean atmosphere.

What should I do if my gas detector readings are different as above?
In both cases first ensure that you make your way to clean atmosphere immediately. Restart the gas detector in the clean atmosphere and check if the unit is now reading correctly. If the gas detector is still reading incorrectly a simple auto-zero may need to be performed (this should be done by a competent person as per the manufacturer’s instructions). If the problem still remains, get the gas detector calibration checked by a competent person.

Can I start my gas detector in any environment?
It is extremely important to start your unit in a clean atmosphere before entering a confined space or potentially contaminated area. The reason for this is that the O2 performs a calibration (and on some models the other sensors perform an auto-zero) upon start-up. If the atmosphere is contaminated the unit will automatically adjust the sensors to the conditions and you would potentially not be warned of the unsafe atmosphere.

What are the settings on the gas detector?
O2 – 19.5% Low, 23.5% High
LEL – 10% Low, 20% High
H2S – 10ppm Low, 15ppm High, 10ppm TWA, 15ppm STEL
CO – 25ppm Low, 50ppm High, 25ppm TWA, 200ppm STEL
Please note that the above settings are the Techsafe standard settings and some companies specify different settings.

What is TWA?
Time Weighted Average. TWA is the amount of gas that a worker must not experience over the duration of a shift. TWA is normally measured over an eight hour shift.

What is STEL?
Short Term Exposure Limit. Some gases and vapours have an allowable maximum STEL which is higher than the 8 hour TWA. STEL values are usually calculated as 15 minute intervals.

What is a calibration?
A calibration is when the sensors in the gas detector are checked against a known gas or gas mixture to see if they are reading correctly.

How often does my gas detector require calibrating?
Every six months.

What is a function or bump test?
This is when the sensors in the gas detector are checked against a known gas or gas mixture to see if they are reading to a specified level within a specified time duration. Sensors such H2S, CO and LEL will only react when exposed to gases which only happens periodically and this is a way of checking that the sensors are operating.

How often does my gas detector require function test?
Manufacturers normally recommend this be done monthly but this is not mandatory.

I only use my gas detector once a year. Does it still need calibration every six months?
Yes. To comply with the manufacturer’s specifications this needs to be calibrated every six months regardless of use.

I only used my gas detector a few times and the O2 sensor now needs replacement. Why is that?
All O2 sensors, irrespective of the make and model of gas detector need replacement every two years. These sensors are of the diffusion type, so they work all the time, not only when the unit is switched on.

My gas detector does not start. It just says “OFF”.
The gas detector will not work if the batteries have little power left. They then automatically switch off and won’t start again unless the batteries are replaced. Replace batteries and try again.

Can I use any battery with my gas detector?
NO. Please refer to the manufacturer’s instructions for the specified type/s. This is essential to ensure your safety in explosive environments. The manufacturers specified battery life is also based on the approved batteries only.

Care and Storage

Care
• Do not spray insecticides on or near the unit.
• Do not clean with anything other than a warm damp cloth.
• Do not use near silicone based products.
• Replace any discoloured sensor screens.
• Keep sensor screens clean and free of debris or obstructions.
• Do not poke holes in sensor screens.

Storage
• Do not store near silicone based products.
• Do not store in direct sunlight (i.e. under windscreen on dashboard).