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The Effects of Temperature, Air Velocity, Humidity, Pressure, and Particulates on Badge Results

Assay Technology badges have been validated to work as claimed under normal office working conditions.  For example, from our  Acetic Acid badge (543) technical insert:

Effect of Temperature: Effect on result < 5% within 0 – 50 C (32 – 122 F).
Effect of Humidity: Functions as claimed within 10 – 80% RH.
Accuracy (MTE): Meets or exceeds OSHA requirements for accuracy:
Maximum Total Error (MTE) < 25% at PEL; < 35% at STEL.

However, frequently we receive inquiries from customers that need to monitor in unusual conditions and they want to know how their environment extremes affect the results.

Particulates:

If you are monitoring in an environment where there are significant dust particles floating around (think particleboard manufacturing, not office building) and the particulates have solid or liquid forms of the chemical you are trying to measure, the results can be affected.

The particles can fall into the badge or stick to the badge.  Then, during storage and shipment, the chemical of interest can offgas out of the particles and into the collection media of the badge, causing a high bias.  By far, the most common concerns are Formaldehyde and Mercury.

We supply particle screens to help, but it is very important to follow the instructions.  Here are some helpful hints:

  • Tell the lab that particle screens were used during sampling.  If you don’t, the lab won’t know to change the sampling rates and your results will be 20% biased low.
  • After sampling, remove the screen in a clean, dust free environment.  If your hands are dusty, you will be leaving dust particles on the badge, causing a high bias.
  • If the report does not say the results were adjusted for the use of a screen, check with the lab to make sure they applied the correction factor to your results.

Air Velocity:

Too Slow

Diffusive monitors need some air movement to work or your results will be biased low.  So, you cannot put them inside your pocket nor under any clothing.  If you are monitoring a basement with zero air movement or inside a cabinet, run a small fan to move the air a bit.  If you are  wearing the badge, there will be plenty of air movement from you moving around  and breathing.

Too Fast?

We tested the badges at air velocities  that are normal for someone walking around.  We are sometimes asked about environments that are very windy.  We believe the badge will work as specified up to very fast air velocities, that is why the media is pressed up against grid face tightly and there is no hole in the back of the badge.

Humidity

There are so many variables here.  The type of badge; the chemical; high humidity; low humidity.  The simplest answer is:  The badge will work as claimed from 10% to 80% humidity.

High humidity

If the badge gets wet and the holes are covered in water, the result will be biased low.  On the organic vapor badge, alcohols with high regulatory limits and lower affinity for charcoal have a higher probability to be affected under very high humidity conditions.  Examples are ethanol and methanol.  To reduce this effect, use our high capacity badge, 546 and sample for shorter time periods.  Alcohols unlikely to be effected at PEL levels because their PEL is so low:  phenol  (525 badge), allyl alcohol.

Low, low Humidity:

At extremely low humidity (less than 10%),  the reaction between the chemical and the aldehyde badges (571 and 581) does not work well.  This RH interference is the same for all tubes and badges that use the DNPH chemistry.  (OSHA 64, NIOSH 2016, OSHA 107, etc)

For the organic vapor badges (546, 566, 525, 574), low humidity is never a bad thing.

Temperature

Way Too Hot

If you melt the plastics, that’s WAY too hot.  266°F (130°C).

Hot

The temperature affects the sampling rate, but very little.  For every 10 degrees Fahrenheit greater than 72 degrees, the sampling rate will increase 1%.  So, if the temperature is 92 degrees F, the sampling rate will go up 2%.  Before you call the lab to have them adjust the data, consider that 2% changes your result from 1.00 ppm to 1.02 ppm.  Significant?  Not likely.

Cold

The effect here is the opposite.  Put the badge in the refrigerator at 42 F, the sampling rate is 3% slower.  Again, significant?  Probably not.

Pressure

This is the high altitude question.  What happens to the results when the sampling is performed in Denver.  A change in pressure does change the sampling rate of the badge.  However, it also changes the molar volume, a value used in the calculations to determine the concentration in ppm.  The good news it the sampling rate speeds up at the same rate the molar volume increases.  So, when reporting results in ppm, there is no effect.

In summary, as long as you:

  • Use a particle screen in dusty environments
  • Don’t freeze the badge in a block of ice
  • Don’t melt it
  • Don’t block the holes in the sampling grid of the badges,
  • run a small fan in areas with stagnant air,
  • use our high capacity, 546, badges when sampling for methanol and ethanol in high humidity

you are very likely to be good to go.  The other effects are relatively minor and unlikely to cause a significant issue.  By all means, give us a call to discuss further if you wish.