There have been so many things going on with our transition into the Enthalpy group of the Montrose family that it has been hard to get anything together in a newsletter and out to everyone. Even with all of those things going on, there have been some important questions that I feel need to be addressed. I hope to do that in this newsletter on hazardous sample shipments.
In talking with a client about sampling flammable gas from a source other than landfills, they mentioned the need to dilute the sample by about half for shipping. However, that dilution is designed for methane concentrations below ~69% and may not give adequate dilution for other sources of flammable gas samples. The question arose again in discussions on developing a new method for monitoring natural gas pipe lines and whether a standard 6 L Summa canister should be required. In all cases of a first sampling event of flammable gases, I would strongly recommend the use of a canister of 5 L, the largest size container which DOT regulations currently allow for flammable gases, or less and shipping that canister as a hazardous shipment, even if it is diluted just to be safe. The results of the first series of analyses can then be used to determine later shipment requirements as desired.
The DOT regulations define a flammable gas as being flammable in a mixture of 13% or less in air. Thus, the way to determine the flammability is to use the formula 0.13X, where X is the concentration of the gas in question, and compare the product with the listed Lower Explosive Limit (LEL) of that gas. The example of this would be a methane source of say 25% being shipped without dilution. This means we multiply the concentration (0.25) by the formula (0.13) to get a concentration of 0.032 or 3.2%, which is below the methane LEL of 5% and thus safe to ship without being labeled hazardous. Now if we have twice the concentration of methane as before we get a result of 6.4%, which is classified as flammable because it is above that LEL of 5%. If that shipment is to be made without being labeled as hazardous, it must be diluted. We dilute in the lab with the assumption the sample will be taken to atmospheric pressure, which is not difficult in this situation because it falls within our normal procedures. Now, if we were going to see a sample with a methane concentration of 75%, our normal procedure would not be sufficient. If we perform the calculation as before we get a value of 9.75% which would require either a greater dilution or the ability to stop the filling of the canister at a point before atmospheric pressure. In this case, if the initial absolute pressure after padding is 325 mmHg and the sampling is stopped at a post–test absolute pressure of 650 mmHg, the concentration of the methane in the sample will be half of what it was and the formula for the determination would give a value of 4.88%, which is below the LEL of 5%. The other option is to increase the initial padding to allow the sample to be collected to atmospheric pressure. If atmospheric pressure is 760 mmHg, that would mean the initial absolute pressure after padding would have to be at least 380 mmHg. Of course, the sampling can also be stopped short of the atmospheric pressure to give an additional buffer for safety. This also would require some additional calculations if there is any minimum sample volume required for a valid sample. In the case of landfill gas that volume is 1 L and that would require the volume of the canister to be at least 2 L in volume if the sample were to be diluted by a factor of two by being half filled with padding gas and sampled to atmospheric pressure. Any container of a larger size may be safely used in place of a 2 L container if the padding is correctly applied, especially if other compounds of interest will need to be reported. As the level of dilution increases so do the detection limits and the only means by which the detection limits may be lowered is by some method of sample concentration.
If we were discussing benzene instead of methane, the results of all of the calculations would be significantly different because the LEL for benzene is 1.2% rather than 5% for methane. This means that an undiluted whole gas sample containing more than 9.23% benzene would therefore be classified as flammable. For any significant concentration of a compound, where reporting other compounds of interest is also necessary, using a container of a size less than 5 L and shipping the sample as hazardous may be the only real option. Canisters are available from us in both 4 L and 4.5 L for situations requiring that a larger volume is taken of the flammable gas, such as the minimum sample rate for Method 25 of 60 cc/min for an hour. That 3.6 L sample volume will fit into either size canister. The larger sized canisters, such as the 6 L, 8 L, 8.3 L, and 15 L volumes can only be used for samples which are not classified as flammable either due to the concentration being too low initially or by additional dilution. If a Tedlar type bag is to be used the largest volume is generally a 1 L, which must be shipped in a hermetically sealed glass or metal container. The most common hermetically sealed container currently used is a 1 gallon paint can with a special plastic seal and a specialized shipping carton.
The most important aspect to remember regarding the shipment of flammable gases is that the shipper bears all responsibility to ensure the regulations are followed correctly for each and every shipment. Any fines for not following the regulations will be levied only upon the shipper. That should be sufficient reason for everyone to err on the side of caution when shipping potentially hazardous samples. None of us wants to see thousands of dollars of fines per container on anyone’s project, especially yours. So if you are ever in doubt about whether a shipment is hazardous, assume it is and ship it accordingly. The cost of shipping it hazardous when it is not is far less than shipping it non-hazardous when it actually is and then being caught. This also means that no laboratory will assume any liability resulting from the improper packaging and shipment of samples.
As is noted by the US DOT in the response to my letters of inquiry on shipping landfill gas samples, they can only agree that, if everything was as I presented it, there would be no issue with the shipments. Since that time, however, there were changes made to the regulations concerning the size of the container which can now be used. While the information here includes all of the current requirements, given the possibility of more changes to the regulations or interpretations thereof, I can make no guarantees regarding the validity of the information presented here for myself or any other entity.
Triangle Environmental Services
122 US Hwy 70 East
Hillsborough, NC 27278