WHY SAMPLE AIR?
Air is all around us. We need it to survive and our environment needs it to sustain life. When we think about the enormous dependency we have on the element of air, one might pose the question: is all air created equal?
We have addressed the quality of air in a previous blog, and in order to accurately illustrate air quality among descriptions within air, we use sampling procedures. Sampling systems are found in many arenas in our culture. For example, samples are taken from biological species at a crime scene during police investigations. Another example, samples are taken in laboratories across the country, daily for medical, technological, and other purposes.
So, what is a sample, and in this context, why sample air?
A sample is often defined as testing or to measure something. However, when running tests or sampling, the object in question is often destroyed or runs a high risk of being altered and changed. We sample air to obtain measurements and identify chemical compound levels within any given sample.
PUMP CALIBRATION AND 8 HOUR VOLUME
Once there is a sample of air, the volume must be accurately known and tested. Pump calibration is a technique used to obtain accuracy of the air sample. This is in part due to air temperate and pressure can alter and skew results. An item called a sampling train, is usually used to connect the pump to the calibrator.
8-hour volume- this calculation allows us to determine how much benzene is present in any given 8-hour time period. To do this, we must make several conversions to get our final solution to represent the units of PPM-parts per million.
Our first calculation would be to multiply our 8 hours (480 minutes) by 2 to get= 960 liters. This represents only the amount of air flowing through the pipe. 960 divided by 1000 will give us the cubic meters answer of 0.96. Then to convert this 0.96 cubic meters into parts per million, we will take the 2.39mg of benzene on tube and divide it by 0.96. Our answer is then multiplied by 24.45 and then divided by 78 which is the molecular weight of Benzene.
Our final answer is ~0.75ppm, which is below the 1ppm by OSHA's standard. This represents that we are underexposed and do not surpass the upper
Time Weighted Average- this is a concept which illustrates a particular concentration of substances expressed over a period of time. This allows for us to understand the overall concentration and then can represent that in OSHA's OEL.
In our above calculation example, our 0.75ppm was our TWA and this provided us a baseline to claim under or overexposure according to the permissible exposure limits by OSHA.
BREATHING ZONE
The breathing zone is particularly important in sampling because it increases the accuracy of the testing procedures. Our breathing zone is subjective and unique to each person. This will determine the amount of exposure (or lack thereof) because our breathing zone moves along with us. So, for an 8-hour period someone may be up on a scaffolding working, while another person may be very close to the ground, kneeling down working on some ground wiring. That's an example of how our breathing zone can influence and effect the results of the sample.
OSHA STANDARD-OEL
OSHA has admittedly reported that they acknowledge many of their permissible exposure limits (or OEL's) are outdated and in need of revisiting and updates. The OEL is a legal limit for exposure in the United States where an employee can safely be exposed to a chemical substance or loud noise.
NIOSH METHOD NUMBER
The use of method numbers allows for classification of substances and organization. Method numbers identify a specific chemical or element and then provide further information on the particular substance.
FLOW RATE, SAMPLE STABILITY, SAMPLE
- Flow rate describes a volume of fluid that passes per unit time, and is often represented by the symbol of Q. (sometimes capital V).
- Sample Stability refers to the un-changing state of a particular sample. Understanding that chemical and biological processes can be altered and changed over time, within the environment or internally. With sample stability we are attempting to hone in on a sample and maintain the integrity of a sample over time.
- Sampler- various equipments used for collection, calibration, and sample testing
- Blanks- Media and Field blanks report varying results depending on substance sampled. They are required so as to provide accuracy in results and to identify potential contaminants during storage and sampling procedures. Minimum of blanks is defined by how many samples are taken during a time period.
