SOP 14. Odor Sampling
Introduction:
This SOP describes the procedure to collect air samples in Tedlar bags
for evaluation in an olfactometry lab.
Equipment:
Teflon tubing ¼ in. I.D.
10 L Tedlar bags with
polypropylene valves
Teflon needle valve ‑
3/8" OD compression fittings similar to Cole-Parmer P/N U‑06373‑30
Teflon tee ‑ 3/8"
OD compression fittings similar to Cole-Parmer P/N U‑06374‑45
Bag
The use of odor free bags is
imperative for determining accurate data. Any residual compounds remaining in
the Tedlar bag could alter the perception of the odor by the olfactometry
panel. The procedure that follows will ensure that reused and new bags are odor
free. New bags will be flushed prior to sampling. The procedure is as follows:
1. Attach sample
line to zero air or nitrogen gas cylinder.
2. Fill the sample
bag approximately 2/3 full.
3. Disconnect
filled bag from gas cylinder.
4. Connect bag to
vacuum pump for purging.
5. Turn on the
vacuum pump and run it until the bag is empty.
6. Disconnect the
sample bag.
Sampling System:
The Teflon tee and needle valve will be installed permanently in the
gas sampling system inside the instrument trailer. The tee is located in the
tubing between the sampling pump P2 (see SOP) and the orifice located prior to
the mass flow meter MF. Advantages for sampling at this location are:
- The tee acts as a flow divider
permitting the same air sample to be used by the gas analyzers and the
odor evaluation.
- The gas analyzers are not
interrupted allowing for continuous sampling.
- Samples can be taken in the
trailer. .
- Inlet pressure requirements (room atmospheric) for the gas
analyzers can be met.
- Collecting samples from inside
the building is not acceptable because of animal disturbance, which would
probably increase the odor emission.
Procedure:
- Eight samples will be collected.
Inlet (background) samples are obtained from the inlet gas sampling tube.
One sample will be collected from each barn air inlet. Triplicate air
samples are obtained at the continuous operating ventilation fan sample
line from each barn. The samples may be taken simultaneously with a
distribution tubing network to each of three tedlar sample bags.
Alternately the samples may be taken individually in succession.
- The bag will be attached to the
discharge side of the needle valve and allowed to fill under the pressure
created by the sampling pump. The needle valve airflow rate is set at 4
L/min. The automatic sampling of the DAQ system will be interrupted during
this procedure and the building sampling location will be manually
selected. A seven-minute purge of the sample lines from each barn location
is required. To reduce absorption losses, 2-4 L of sample air are
introduced into each bag and removed before filling the bag with sample
air.
- If the sample bag is to be air
transported, the bag should be filled to 80% capacity to prevent the bag
from exploding at reduced atmospheric pressure. During cold weather
sampling the bags should be stored and transported at temperatures similar
to the exhaust air to prevent condensation.
- The bag should be labeled with
the following information:
- Sample source
- Sampling location
- Sample time and date
- Sampling start time
- Sampling stop time
- Person taking sample
- Any unusual
conditions or observations
- Other information
specific to local lab requirements
- Chain of custody
with signatures
Alternative Bag Sampling Procedure using Pump and
Vacuum Chamber
An air pump and a vacuum chamber will be used to fill the bags. The air
pumps will be comparable to SKC Model 224-PCXR8 (SKC, Inc., Eighty-Four, PA) or
the 1.0 to 6.0 L/min, constant airflow AirPro Model 6000D (Bios International
Corporation,
The SKC Vac-U-Chamber will be used to fill the sample bags using the
air evacuation method. It is a rigid air sample
box which allows the direct filling of an air sample bag using negative
pressure provided by most personal gas sampling pumps. When using the
Vac-U-Chamber, the air sample enters the bag directly, without passing through
the pump. This eliminates the risk of contaminating the pump or the sample. The
Vac-U-Chamber has rigid walls which will not collapse under vacuum conditions,
thus eliminating possible errors. All surfaces in contact with the sample are
constructed of stainless steel, Teflon or Tedlar.
1.
Place bag inside VAC-U-Chamber with the fitting
on the right hand side.
2.
Connect the valve on the bag to the Teflon tubing
inside chamber.
3.
Set pump to a flow rate of 3 L/min.
4.
Connect pump tubing to chamber vacuum valve via
male quick disconnect.
5.
Open the valve on the Tedlar bag two turns
counterclockwise.
6.
Close and latch chamber.
7.
Close decompression valve.
8.
Secure sample tube at sampling location.
9.
Turn on pump for approximately one minute to
fill the bag 1/3 full.
10.
Disconnect sampling tube from sampling location.
11.
Open decompression valve, latches and chamber
lid.
12.
Remove pump tubing from vacuum valve and attach
to purge valve.
13.
If not already done, turn Teflon tube to the
horizontal so that it will not inhibit evacuation.
14.
Detach sampling tube and cover sampling line
inlet on the VAC-U-Chamber.
15.
Start pump.
16.
Run pump until bag is empty.
17.
Reconnect pump tubing to chamber vacuum valve.
18.
Close and latch chamber.
19.
Close decompression valve.
20.
Reattach sampling tube to sampling location.
21.
Turn on pump for 3 minutes to fill bag to
approximately 2/3 of the volume.
22.
Turn pump off.
23.
Open VAC-U-Chamber.
24.
Close the valve on the Tedlar bag completely before
removing the bag.
