Wayne’s NoTes December 2015 (version 1)

After my last newsletter on shipping potentially flammable gas samples I was asked about compounds other than methane and how those could be shipped. One question that came up several times was the possibility of a spreadsheet that could be used to calculate shipping dilutions, etc. by anyone. I looked into such a spreadsheet but there were more issues than I expected when it was first conceived. The biggest issue turns out to be liabilities in creating such a program to determine how much to dilute a sample. The other issues are not as large but they are significant on their own. Trying to determine a valid pressure dilution before the sampling is a little easier than after the sample is taken due to the pressure upper limit for a gas sample, but everything still had to be calculated in absolute pressures. This is further complicated if there is more than one compound in the sample stream which could be flammable because that affects the calculation of the explosion limits from which everything else is determined. After much head scratching and just a little more hair loss on my part I came up with a compromise that I hope helps but is not specific to any situation or sample.

The first column is, of course, the name of the compound to be shipped. This was a list of flammable gases from a specialty gas provider and hopefully covers most of the compounds of interest. The second column is the percentage Lower Explosive Limit (LEL) for that compound from my CRC handbook. The third column is the calculated maximum concentration of only that compound which can be shipped as a sample with air or an inert gas as the balance. This calculation was taken out to eight decimal places to help flag this as only an estimate. Having so many digits passed the significant digits should, I hope, be a flag to remind everyone of the variability of such a calculation and the need for a safety factor buffer.

For example the first compound listed is acetone, which has a listed LEL of 2.6%. This means that by using the U.S. DOT formula stating that 13% of the contents of the sample mixed with air must not be flammable in order to be shipped as a non-flammable sample. Using the sample concentration, which would be the first to be classified as flammable as a variable and solving for it, we can determine the maximum concentrations for any individual compound. This means any concentration of less than 20% should be capable of being shipped without any special handling or procedures. Anything over 20% would not be legal to ship without special handling or some type of dilution.

The fourth column details the maximum calculated concentration of each specific compound which should be legal to ship as non-hazardous with what would be a 5 times dilution applied. The fifth column details the maximum calculated concentration which should be legal to ship as non-hazardous with a 7 times dilution applied. I also applied a little color coding to the list. The green indicates a compound which should always be a legal shipment as non-hazardous with no more than a 5 times dilution applied. The yellow indicates a compound that should almost always capable of being legally shipped as non-hazardous with a 5 times dilution applied. The black indicates a compound which should always be capable of being legally shipped as non-hazardous with a maximum of a 7 times dilution applied and the red is a compound which may require a dilution greater than 7 times in order to legally ship as non-hazardous.

It is possible to add other compounds to the list as long as you have the LEL from which to determine the calculated concentrations based upon the U.S. DOT formula. Again, I want to ensure the knowledge of the large number of variables which may play a part in these shipments. This list is a good guideline, but if there are multiple compounds involved or the calculated concentrations are close to the limits please exhibit caution. Most of these types of samples are not going to injure or kill anyone, but they can be a violation of the regulations and as such can result in fines that will significantly injure the bottom line of any project and possibly other projects too.

I have included the spreadsheet as a separate attachment if you wish to download it for review and use.

Wayne Stollings

Triangle Environmental Services

122 US Hwy 70 East

Hillsborough, NC 27278