Passive Air Sampling- what is it and why do we need it?

Passive air sampling should be part of every workplace safety culture when working around hazards. When that hazard is an invisible, airborne gas, passive air samplers are imperative in keeping your work environment safe. Passive air sampling is a method of testing for air pollution and harmful chemicals such as carbon monoxide and other organic compounds. Unlike active air sampling, which requires you to have a bulky pump, and glass tubes to act as a sorbate, passive air sampling uses a smaller device, about the size of a credit card, which can easily clip on to a shirt or a stand. It is necessary to ensure the health and safety of engineers, technicians, and bystanders at work sites.

Who makes air samplers?

A few companies have historically produced passive air samplers for the workplace safety market. SKC stands above those companies in innovation and technical knowledge. They have moved the industry past the use of tubes, and over to much more manageable badges. You can use the badges multiple times over an extended period in contrast to one-use tubes.

How it works (What is diffusion?)

The passive air sampler is a small measuring instrument. It can be a badge, a tube, or a canister. The sampler has a diffusive coating (hence their other name, diffusive samplers). Underneath this coating is a sorbent material which absorbs the airborne gases. This occurs according to Fick’s laws. Fick’s first law states a gas will move from an area of high concentration to an area of low concentration, Fick’s second law says all gases will act in this way independently of each other. The makeup of the sorbent causes a chemical change in the gas when it absorbs into the sampler. A lab can then examine the device, measuring the presence of air pollution spectrographically using other chemicals as reactants.

When do I use it?

You can use Passive air sampling anywhere there is concern about air pollution and hazardous gas contamination. You should also be using it where active air sampling will not work, for example in confined spaces. Your use of passive air samplers may also be necessary due to OSHA requirements. Diffusive samplers can detect organic compounds such as carbon dioxide, or formaldehyde. They may also disclose the presence of inorganic gases such as ozone, or mercury, depending on the sampler. If you have the correct sampler and proper sorbent, you can test for just about any form of air pollution.

Benefits and drawbacks of Passive Air Sampling

What are the benefits of diffusive air sampling?

  • Your equipment is much more compact and portable.
  • The equipment used in passive air sampling is much cheaper than that used in active air sampling.
  • You’ll spend less time spent training.
  • Workers find them easier to use.
  • You have more flexibility with samplers, and you can use short term or long-term

What are the downsides of passive air sampling?

  • You cannot measure air flow, therefore the manufacturer needs to supply a validation report
  • More sensitivity to the conditions you use it. Unlike active air sampling, the wind is necessary, but they will not operate if there is too much wind.
  • When you use a passive air sampler it may not be sensitive enough. In these cases, it will not be approved for use.

The history of passive sampling

Technicians and engineers have been trying to monitor for hazardous gasses since at least 1853. Back then they put filter papers filled with potassium-iodine on the ground to test for the presence of ozone. Much later, in 1927, Gordon and Lowe registered a patent on a colour change test which captured Carbon Monoxide. This test utilized palladium oxide as the sorbent.

It wasn’t until 1973 that the first modern passive sampler appeared. E.D. Palms and A.F. Gunnison brought it to market. This passive sampler used a mercuric chloride solution in a tube as a sorbent. It detected the presence of carbon dioxide using a colormetric scale. The value of this technology in detecting gases in high risk environments was demonstrated by these tubes. It wasn’t long before these “Palmer tubes” were developed for the detection of other gases, such as nitrogen dioxide and ammonia.

Over the course of the ‘80s and ‘90s more sorbents were becoming available. By the turn of the century thermal desorption, a process by which heat is used to make contaminants more volatile, was being used in passive air samplers.

Conclusion

The concept of passive air sampling has existed for a very long time. Even so it is only in the past 30 years that the technology has matured. Passive sampling technology has now become a viable alternative for active air samplers. Although there are still situations where a passive air sampler will not work as well as an active sampler, these situations are becoming rarer. An integral part of a healthy safety culture, and capable of meeting OSHA requirements, these devices continue to make our professional lives safer.

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April 24, 2019
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