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Sampling Suggestions & Containers

Many times the Fire Investigator is only able to obtain samples of Fire Debris often weeks after the event took place. After the heat of the fire, the dilution by extinguishing practices, and further weathering by environmental and sometimes microbial factors, the samples are often both very weak and very weathered. Activation Laboratories has continually advanced the science to improve both the sensitivity and focus of the method for the detection of flammable liquids in order to provide the best analysis for these weak samples.

At these low concentrations the background of hydrocarbons from newly purchased mason jars can complicate the analysis. These hydrocarbons are in the medium to low parts-per-billion range which can be detected by our method. This sensitivity most likely exceeds the capability of other laboratories. The hydrocarbons are on the glass surface and surfaces of the tin lid. Through our testing we believe that the source of these compounds is from the manufacturing process, the cardboard shipping material and from contamination of the cardboard during shipping from the manufacturer. We do not believe this contamination to be from the red sealing ring although this may have been a problem with older jars having separate seals. To improve the analysis of weak samples, we have devised a simple method of cleaning the mason jar and lid that the Fire Investigator can do prior to going out to the field site.

After purchase of the mason jars (any brand or size) we highly recommend the following procedures:

  1. Transport of boxes in the passenger compartment instead of the trunk whenever possible. Protect the cardboard box(es) from any further contamination.
  2. Run cold tap water for one full minute. Then rinse a kettle that you usually use for boiling water and proceed to boil about half a kettle full. While waiting for it to boil, set up batches of six bottles.
  3. After boiling, pour in just enough hot water to fully cover the bottom of the mason jar. Do this for each jar in one batch of the six jars at a time.
  4. Put the lids & locking rings on the jars, then shake the jars 5 times so the water contacts all surfaces.
  5. Carefully remove the locking ring and lid. Pour the water down the sink drain, then let the jars cool (don’t turn upside down). Put the lids on a paper towel with the inside face up to air dry.
  6. When the each lid and jar has fully cooled, drain and shake the excess water from the jar. NOTE, some moisture droplets of this distilled water that is left in the jar is okay.
  7. Assemble the jar, lid and locking ring. Tighten the ring only loosely and store in the shipping box.


It is important to note and document on transmission sheets sent to the laboratory whether this cleaning procedure has been completed on the jars used for sampling. This cleaning procedure is especially important when the sample may be weak and contain highly weathered gasoline or highly weathered fuel oil. This procedure improves the probability of finding a positive result in this type of sample by approximately a factor of five. In cases where the cleaning procedure has not been documented, the laboratory will have to apply a higher safety factor in the interpretation of results which may potentially lead to a false negative result.

More recently we have tested a new quart size tin paint can for comparison as this is also used in sampling. The unlined paint can also has a hydrocarbon background. This background is just less than a non-cleaned mason jar but significantly greater than a mason jar cleaned using the above procedure. The formation of rust precludes cleaning the paint can. Rust is also evident in the paint can, having a sample, after only 4 days of storage. "Nylon" evidence bags are excellent with regard having a low background for hydrocarbons.

We recommend using nylon evidence bags or a pre-cleaned mason jar, using the above procedure. The mason jar allows for longer sample storage, easier analysis and better sample integrity than a nylon bag or tin container.

Activation Laboratories Ltd. | 41 Bittern Street, Ancaster, Ontario, L9G 4V5, Canada | TF: +1.888.228.5227
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