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* Never reuse a Tedlar bag when sampling for ppbv level compounds. 4.1.3 Hold Time for a Tedlar Bag The media hold time for a Tedlar bag is indefinite if stored out of sunlight in a cool, dry location. Tedlar bags can be used to collect samples containing common solvents, hydrocarbons, chlorinated solvents, sulfur compounds, and many other classes of compounds. The sample hold time to analysis varies for different classes of compounds: • 24 hours: Sulfur compounds (e.g., hydrogen sulfide and methyl mercaptan) and chemically active compounds (e.g., 1,3-butadiene). • 72 hours: Chlorinated solvents, aromatic compounds, and atmospheric/fixed gases (oxygen, nitrogen, carbon dioxide). 4.2 Tedlar Bag Sampling Using a Tedlar bag to collect an air sample normally involves ' "active" sampling, unlike an evacuated canister that can be tilled"passively"by simply opening the valve. There are two methods commonly used to fill a Tedlar bag: using a pump or a lung sampler. 'W • Sampling with a Pump: The most common method to fill a Tedlar bag is to use a small pump with low flow rates (50-200 mL/min) and tubing to fill the bag. Air Toxics Ltd. does not provide pumps but they can be rented from equipment providers orpurchased from manufacturers such as Neuberger or Gilian. Pump • Sampling with a Lung Sampler: Alterna- Sampleedd Air to tively to using a pump, a "lung sampler" can be used to fill a Tedlar bag. Although a little more complicated than simply using a pump, the main advantage to using a lung sampler is that it avoids potential pump con- tamination. A Tedlar bag with attached tubing is placed in a small airtight chamber (even a 5-gallon bucket can work) with the tubing protruding from the chamber. The sealed chamber is then evacuated with a pump causing the bag to expand and drawing the Sealed sample through the protruding tube into the bag. The Chamber sample air never touches the wetted surfaces of the pump. Air Toxics Ltd. does not provide lung samplers, but they can be rented from equipment suppliers or 9 AIRTOXICSLTD. 17