ENVE 649, Module 4, Closure
From Quiz.
***STEL= Short Term Exposure Limit. This is the concentration that should not be exceeded, averaged over 30 minutes. Regarding the STEL and Ceiling limits, real time monitoring is needed, usually some type of alarm. Draeger tubes could perhaps be used, if the air concentration was likely to stay constant, but the passive monitoring tubes are only useful when evaluating longer term exposures.
*** Q. I would add to my discussion about the unclear sections the part about where Draeger tubes are different from other colorimetric tubing.
A. "Draeger" is used for tubes as "Xerox" is used for copiers. There are several tube manufactures. However there is a big difference between "passive monitoring" tubes and the standard Draeger tube. The later requires you to pump air through and it gives an immediate result. Passive tubes must be worn for the stated length of time, often eight hours, to give a result.
**Q. When reading web sites about equipment types, used for working place monitoring, I understood that this part of module is not so easy as it comprises a really huge amount of information…
A. Yes, and that is part of the point. There are many types of protection and monitoring devices. You start by understanding WHAT you are monitoring for or protecting from. Then go from there.
**Q. The confusing part for me was the details of air sampling and direct measuring. It is not stated that which method is better if we have to make a law for emission of a certain material. Which one gives more accurate results? I understood in urgent situation we use direct reading but what if we have to decide emission for a factory.
A. Emissions from the factory, like up the smokestack, are an environmental air pollution issue, not a worker health issue. They come under the clean air act, which we will briefly cover later. The CAA has specifications about monitoring the stack emissions. The take home message from this module is that there are many types of monitoring devices. You need to understand the chemical you are monitoring, and the circumstances under which you will monitoring. (You also need to know if it comes under a particular law, and if that law has specifications about monitoring.)
Q. This is a sentence directly from the SKC site pertaining to their diffusion tube. "Using the principles of gas diffusion and colorimetric reaction, Dräger Color Diffusion Tubes allow the user to reliably measure Time-Weighted Average (TWA) concentrations for up to eight hours." ---The indications for the product do not limit the use of the product to any length of time. The product does not have a minimum time requirement for the use of the product. I feel that the instructions could be defined for its use to evaluate a STEL. "When using Diffusion Tubes, the Time-Weighted Average (TWA) can be calculated at any time during the measurement by simply dividing the length of the tube reading (in ppm-hours) by the elapsed sampling time (in hours)". Since 15 minutes is within the 8 hour maximum and can be represented in hours as 0.25 hours, I felt confident in my answer for question #4. which ended up being wrong .
A. OK. I'll give you credit for that, based on your reasoning. You could use them for that. I emailed SKC to ask their advice. Regular Draeger tubes are for spot readings and are OK for STEL. For the diffusion tubes you would have to divide by ¼ hour. That seems too coarse, keeping in mind that the tubes are only good for +/- 25% anyway. I was trying to contrast these with the regular Draeger, but you're right, in theory you could use these for that.