How gas detection makes your workplace safer

CAC Gas & Instrumentation

Tuesday, 15 January, 2019


How gas detection makes your workplace safer

How important is it to check your gas detection device?

According to NIOSH, atmospheric hazards account for 40% of the deaths in confined spaces.

OSHA found that oxygen deficiency or gas poisoning accounted for a similar percentage of deaths in industry. OSHA stated that asphyxiation was the main hazard in confined spaces, and that atmospheric hazards were the leading cause of death.

Individuals still take their life in their own hands by not taking the small amount of time and cost to properly check their gas detection device prior to entering hazardous environments.

The top eight reasons your gas detector won’t work

1. Environmental

Dirt, dust and water impact. These physical effects can block gases and vapours from entering the sensor chamber preventing detection of the gases. This can be either within the sensor area, sampling pump or sample lines.

2. Physical effects

Dropping and other abuse can prevent the instrument from working properly or alter the ability of the detector to measure accurately.

3. Gas exposure

High gas exposure will change the calibration curve of the sensors, causing false or inaccurate readings. Extremely high concentrations can kill the sensor’s ability to measure gas. Many sensors can fail but not provide a warning that they have failed. In fact, many provide a zero indication on the meter reading, which suggests they are working correctly when they are not.

4. Catalytic sensors affected by poisons and inhibitors

Catalytic combustible gas sensors can be poisoned by silicone-based compounds and airborne lead. These kill the sensor. Inhibitors such as sulphur compounds and chlorinated compounds reduce the sensor’s ability to measure, slowing the sensor’s response and, in some cases, reducing the sensor’s ability to measure some gases. For example, being able to measure pentane but not methane due to the reduced sensitivity.

5. Electrochemical sensor poisoning

In this case sensors can be poisoned by other gases which are adsorbed into the sensor chamber and react with the electrode catalyst.

6. Temperature effect

Storing instruments in an environment which is either too cold or too hot can affect the ability of the sensors to measure accurately.

7. Moisture

Moisture condensing on or in the sensor. This can happen to oxygen sensors when moisture condenses in the capillary tube in the sensor. It will cause the sensor to fail.

8. Calibration drift

All sensors from all manufacturers drift over time. Calibration brings the sensor back into equilibrium and provides accurate readings.

How do I make sure my sensors work?

The only way to guarantee that a gas detection instrument will detect gas accurately and reliably is to test it with a known concentration of gas. Exposing the instrument to a known concentration of test gas will show whether the sensors respond accurately and whether the instrument alarms functions properly.

Q: Do I need to use test gas?

A: Yes, testing your gas detection instrument with test gas is the only way to ensure the gas detection device is working correctly and that you can be confident it will measure the atmosphere you are working in.

How do I test my gas detection instrument?

Here are the terms used in the industry for ways of testing your gas detection instrument:

  • Calibration
  • Verification
  • Bump testing
  • Function testing
  • Challenge testing
  • Response testing

What do these terms mean?

The above terms are used by the gas detection industry globally, but the definitions of these terms are inconsistent. In fact, the term ‘bump testing’ can be defined differently from one person to the next. This is a major cause for concern as it creates confusion. Here we will define calibration, verification and bump testing and note when the other terms are used.

Instrument verification

Verification is the process of determining whether the instrument is still accurate and is within accuracy requirements for all sensors. The process does not make any instrument adjustments but rather compares the instrument response to a known concentration of test gas over a specific length of time.

Provided the response reaches a satisfactory level relative to the test gas (+/-) then the instrument is considered accurate and is ready for use. The customer would determine what level of accuracy was acceptable (example +/- 10%). Typically, this would take 90+ seconds depending upon sensor type.

Should the sensor fail to respond to a satisfactory level then the instrument should be taken out of service and sent for calibration. The terms function test, functional bump test or response test are often used for this process. AS/NZS 60079 uses the term ‘response check’ to describe this test.

Gas calibration

Calibration is all about accuracy. Calibration refers to an instrument’s measuring accuracy relative to a known concentration of gas. Calibration determines the relationship between an instrument’s readings and actual concentration of the component gas of interest.

The more accurate you want your instrument the more often you will calibrate it. Issues affecting sensor performance noted above will also determine frequency of calibration. Your application should determine calibration frequency.

Calibration requires adjustment of the instrument either manually or automatically and therefore should be limited to those with appropriate training or via pre-programmed calibration systems.

Bump testing

The term bump testing is now used globally but is defined differently by many users which can cause confusion. It is important that all employees are clear on what is required when using the term ‘bump testing’ in order to prevent miscommunication and misunderstanding in the workplace which could lead to a fatality.

  • Common definition #1: Bump testing is the process of applying a test gas to the instrument and observing that each sensor responds to the gas with their reading increasing (LEL, toxic sensors) or decreasing (O2) and that all alarms, both visual and audible, turn on. This demonstrates the overall operation of the gas detector but does not check the reading response for accuracy. This test confirms that the instrument will detect gas in the workplace. This type of bump testing is really confirming the instrument works. The typical length of the time this test takes would be around 30 seconds depending upon the sensor type.
  • Common definition #2: Several standards and resource materials define the term ‘bump testing’ for the process defined above as ‘verification’. In this case they are checking for accuracy of the sensors where in definition #1 they are not.

Q: How often should I bump test?

A: Prior to every use.

All gas detection devices must be calibrated regularly, and function/response tested prior to use for maximum accuracy and safety.

CAC Gas & Instrumentation specialises in specialty gas products for gas detection, process gas analysis, and environmental monitoring and laboratory gas analysis applications.

Image credit: ©stock.adobe.com/au/chanjaok1

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