Most landfill samples will be at a concentration of methane that would be considered flammable. The DOT regulations on shipping non-pressurized flammable samples require the container to be less than 5L, regardless of the pressure of the sample inside. The samples would have to be marked hazardous, complete with the extra handling and fees associated. The other option is to dilute those samples to the point at which they are no longer flammable.
The tanks for 3C/25C sampling are typically sent out with a partial pressure of helium in order to dilute the methane concentration to a point determined by DOT regulations as non-flammable. This is roughly half full. This means that a 4L tank will have approximately 2L of helium and approximately 2L left for sampling. This is not an exact amount, which should be taken into account if compositing.
Other compounds may require differing amounts of dilution in order to be considered non-flammable. The proper calculations should be performed when necessary. There is a link at the bottom of the page for the letter we have on file from the DOT regarding the shipping of samples and a link for a calculation spreadsheet for other compounds.
Cfr regulations on flammable gases:
49 CFR 173.306.(a).(4).(iii) Non-pressurized gases, flammable must be packed in hermetically sealed glass or metal inner packagings of not more than 5 L (1.3 gallons) and overpacked in a strong outer packaging.
49 CFR 173.115.(a) For the purpose of this subchapter, a flammable gas (Division 2.1) means any material which is a gas at 20 °C (68 °F) or less and 101.3 kPa (14.7 psia) of pressure (a material which has a boiling point of 20 °C (68 °F) or less at 101.3 kPa (14.7 psia)) which—
(1) Is ignitable at 101.3 kPa (14.7 psia) when in a mixture of 13 percent or less by volume with air; or
(2) Has a flammable range at 101.3 kPa (14.7 psia) with air of at least 12 percent regardless of the lower limit. Except for aerosols, the limits specified in paragraphs (a)(1) and (a)(2) of this section shall be determined at 101.3 kPa (14.7 psia) of pressure and a temperature of 20 °C (68 °F) in accordance with the ASTM E681-85, Standard Test Method for Concentration Limits of Flammability of Chemicals or other equivalent method approved by the Associate Administrator. The flammability of aerosols is determined by the tests specified in paragraph (l) of this section.
The calculations link below will download a spreadsheet with information on different compounds and their required dilutions for shipping. The calculations are provided for information only and do not guarantee DOT compliance.