AT Lab Report - Frequently Asked Questions
|What do all the columns on my report mean?|
| We have several report
formats. But this describes our most common report.
|Equations used to determine the Exposure:|
Quantity Found (ug) on media
Exposure (ug/L) = ---------------------------------------------------------
Sampling Rate (L/min) X Sampling Time (min)
1 mg 1000 L
Exposure (mg/m3) = Exposure (ug/L) X -------------- X ------------------
1000 ug 1 m3
Molar Volume 24.1 (L/mole)
Exposure (ppm) = Exposure (ug/L) X --------------------------------------------------
Molecular Weight (g/mole) of Chemical
Assay Technology, Inc. uses the Molar Volume at 22 C because most work places are closer to this temperature. The sampling rate is either the flow of air through an active sampler (cassette, tube) or the sampling rate for a specific chemical on a diffusive sampler. Need a sampling rate for a diffusive sampler?
|Which column has the data that I am looking for?|
|In most cases, it is the Concentration/Exposure (ppm) column. If you are monitoring for an analyte that has a regulatory limit in mg/m3, then you will need to look at the "Concentration/Exposure (mg/M3) column.|
|Is the Exposure a "TWA?"|
|The exposure on our report is the analyte's average concentration in the air for the period of time that was monitored. It is NOT necessarily an 8 hour time-weighted average (TWA). It is an 8 hour TWA only if you monitored for 8 hours. If you want to convert the exposure to an 8 hour TWA and do not know how, please call for Technical Support at 800-833-1258. Based on what you know about the environment that was sampled, you will need to decide what happened while you were not monitoring. For example, if you monitored for 5 hours, then what happened during the other three hours? Do you expect the exposure rate would not change or did any possible exposure end?|
|Is the Reporting Limit (ppm) the Regulatory Limit?|
|No. The reporting limit is the lowest concentration that the analyte would have to be present in order for it to be detected by the instrument. It is our goal to have the reporting limit be ten (10x) times lower than the applicable regulatory limit. So, it is very possible for an analyte to be detected, but not be over the regulatory limit.|
|Why do the reporting limits vary on my samples?|
|The reporting limit will vary on samples because it is a function of time.
The longer the sample time, the larger the sample volume, which increases
the sensitivity of the badge, providing a lower reporting limit. Conversely,
a shorter sample time will results in a smaller sample volume, and higher
For diffusive monitors, the reporting limit for each chemical on the same monitor will vary as well. Chemical diffuse into the monitor at different rates. A big molecule will diffuse slowly. While a small molecule will diffuse relatively quickly. So the sampling rate will vary depending on the chemical, which means different sample volumes, which means different reporting limits.
|What is Quantity Found (ug)?|
|This is an intermediate measurement used in the calculation of the exposure. It is not to be compared against a regulatory limit. The quantity it is referring to is the amount of the analyte that was found on the sampling media in micrograms (ug). Once this number has been determined, the sampling time and sampling rate of the badge are applied to calculate the exposure (ppm).|
|What does "ND" mean?|
|ND stands for None Detected at or above the reporting limit. In other words, the concentration was so low that the instrument could not detect it.|
|My result is over the regulatory limit. What do I do now?|
|It is Assay Technology’s intent to provide smart, effective products and services that people can utilize in their health and safety plan. We are not in a position to be able to manage a company’s safety concerns. However, frequently, customers choose to: monitor the area of concern again, reevaluate their safety equipment (hoods, etc), reevaluate their procedures, and/or hire a safety consultant.|
|Why aren't the Regulatory Limits on the reports?|
|Regulatory Limits are on the reports for some of the most requested analytes: Formaldehyde, Glutaraldehyde, Ethylene Oxide and Nitrous Oxide. However, there are too many chemicals and limits for us to manage. Your best source for regulatory limits is from OSHA itself. Both OSHA and NIOSH have very helpful websites. You can access them through our Related Links page.|
|My result is so high, I suspect there may have been an error. What could have gone wrong with the monitoring?|
|It is important to thoroughly explore the possibility that there is no error and the concentration reported properly reflects the concentration of the chemical in the air. However, errors certainly are possible. For diffusive monitors (badges), probably the most common error that leads to a very high result is when the badge is splashed with the chemical. Even a tiny droplet can cause a significantly high result. Also, if someone touches the badge while they are working with the chemical of interest, a falsely high result is possible. These errors tend to lead to extremely high results. Other errors, like not handling the monitors as specified by the manufacturer are possible and can also cause results to be biased high. Certainly it's possible there was something wrong with the sampler itself or with the analysis at the lab. Obviously we work very hard to make sure this does not happen. However, we are happy to investigate your concerns when they come up.|
|What impact does "Sample received without the sampler cap in place" have on a sample?|
|To begin sampling, the sampler cap is removed to expose the badge to the air. Once the exposure is complete, the sampler cap should be snapped back onto the badge to stop it from further sampling. If the sampler cap is not put back on the badge, then the badge will continue to monitor the air that it is exposed to, causing a high bias if it is in an area that contains the chemical you were monitoring. If you immediately put the uncapped badge into the return container and/or into a sealed return envelope, then the high bias is likely to be extremely low (insignificant). When a badge is received without its sampler cap, we flag the results to alert the customer that there was a sampling procedure error. If the result seems normal and/or well below limits, it is reasonable to assume that the result was not significantly affected.|
|What does the message "Caution: Sample not returned within Manufacturer's Maximum recommended Holding Time" mean?|
Most chemicals are not stable on sampling media indefinitely. There is a length of time between sampling and analysis where the accuracy of the result might be affected due to chemical breakdown, reverse diffusion, etc. Based on storage stability data for a particular monitor, samples that arrive back to the lab after the recommended holding time has been exceeded are flagged with a note to use the data with caution. In many cases, it is not possible to determine exactly how much the results have been affected. However, a badge that should have been returned within a week, but was stored in a freezer for 2 weeks before it arrived at the lab will be less affected then a badge that was stored for 2 weeks in an unconditioned warehouse in the summer. Recommended holding times are listed on the technical inserts included with all Assay Technology products. They are also available online.
|Why does the result say "VOID?"|
|When each sample is received, it is checked to see if it is in good condition. If there is a significant problem and any result that would be obtained from analyzing the sample would be severely compromised, then the lab will not proceed with the analysis. When this happens, the report will read "VOID" in the quantity found column and no exposure will be given.|
|What does sample capacity mean? What is ppm-hr?|
Sample Capacity is a measure of the amount or exposure of contaminant that a Sampler can collect without becoming saturated.
Sample Capacity is often stated as the number of micrograms of a particular Contaminant that can be collected on a particular Sampler. For the field IH practitioner, an equivalent (and more meaningful) expression of exposure can be derived by stating the contaminant concentration multiplied by the number of hours of sampling that can be conducted at that concentration. In the Laboratory, the total contaminant exposure (in ppm-hour) is computed from the Sampler’s contaminant loading (in microgram) from an equation using empirical constants. The contaminant concentration (in ppm) reported by the Lab is computed from the exposure (in ppm-hr) divided by the exposure time (in hr). Thus, Sample Capacity can be expressed either in “micrograms” of contaminant or in “ppm-hr” of contaminant exposure.
Hence, the statement: “The Sampler is able to sample at least 10 ppm for at least 8 hours (80 ppm-hr) without becoming saturated.”
Testing to confirm the Sample Capacity is usually conducted by exposing the Sampler in a chamber to specific contaminant concentrations (ppm) and times (hr). As long as the plot of “micrograms contaminant found” (on the Sampler) versus “ppm-hr” (of contaminant exposure) remains linear, that amount of exposure (whether in ‘micrograms” or “ppm-hr”) is understood to be within the Capacity of the Sampler for that Contaminant. In many cases, the Sample Capacity has been stated as “greater than” ( > ) the highest contaminant exposure that has been verified in the lab. In these cases, the actual Sample Capacity may be much higher than the value in the table.
The Sample capacity is listed on the technical inserts that come with the product and can be found on the website. Technical Inserts