1.0 PURPOSE
The purpose of this procedure is to provide written instructions/guidelines for sampling most gases and vapors for Nitro Construction Services Sorbent tube sampling is the NIOSH/OSHA approved method for collecting most hazardous gases and vapors from the air.
2.0 EQUIPMENT
2.1 An air-sampling pump capable of sampling at the recommended flow rate with the sampling medium inline
2.2 Airflow calibration unit (The calibration unit needs to have the proper flow cell to calibrate the pump at the recommended flow rate )
2.3 Sorbent sample tubes with end caps
2.4 Tube breaker
2.5 Tube holder or protective tube cover
Note: If using a universal sampler (a pump that is capable of operating in a low or high flow mode, above or below 750 ml/min.), use an adjustable low flow holder for sampling at flow rates below 750 ml/min; a low flow holder is not necessary for flow rates greater than 750 ml/min. If using a low flow sampler, it is not necessary to use a low flow holder. To determine the correct flow rate for the chemical being sampled, refer to the appropriate NIOSH/OSHA analytical reference method.
3.0 PROCEDURE
3.1 Preparing the Sorbent Tube
3.1.1 Use a tube breaker to break both ends of a sorbent tube to provide an opening at least one-half of the internal diameter of the tube.
3.1.2 This tube will be used for setting the flow and not for collecting the sample.
3.2 Setting Up The Sampling Train
3.2.1 With Low Flow Holder – If using a universal pump, ensure that it is in the low flow mode. With the flexible tubing, connect the low flow holder to the pump intake. Place the sorbent tube into the black rubber sleeve of the low flow holder. The printed arrow on the sorbent tube shows the direction of the airflow and should point toward the pump. If there is no arrow on the sorbent tube the sorbent sections should be closer to the pump.
3.2.2 Without Low Flow Holder – Using a low flow pump, connect the flexible tubing from the pump intake to the tube holder. Place the sorbent tube into the black rubber sleeve of the tube holder.
3.3 Setting the Flow Rate
3.3.1 To measure the flow rate, connect the open end of the sorbent tube to an external flow meter. Set the flow rate specified in the analytical method for the chemical being sampled.
3.3.2 Conditioning the Flow Tube – Turn on the sampler. Depress the Bubble Initiate Button several times to wet the inner walls of the flow tube. You will not be able to initiate a timing bubble without first “priming” the flow tube.
3.3.3 Power Up – After the flow tube walls have been “primed”, turn on the power switch of the Electronic Bubble Meter Base. Wait approximately 10 seconds while the system runs through its check sequence. The run LED will light at this time as well as a LO Battery indication and a series of five dashes displayed in the LCD readout. Do not operate the Bubble Meter until the Run LED signal extinguishes.
3.3.4 Bubble Generation – For optimum bubble generation, depress the Bubble Initiate Button and hold to initiate one (1) bubble up the flow tube. Release the button to initiate a second bubble up the flow tube. This will be the standard procedure to make clean, consistent bubbles at high and medium flow ranges.
3.3.5 Calibration of Sampling Pump – Initiate several bubbles up the flow tube to see what flow rate at which the pump is operating. Adjust the flow rate by turning the flow rate adjustment screw and re-initiate a bubble up the flow tube. When the pump is at the required flow rate for the gas or vapor to be sampled, take three readings for a pre-calibration before placing the pump on an individual. Add the three readings together and divide by three to obtain the average flow rate.
3.4 Sampling
3.4.1 When ready to start sampling, break open both ends of the new sorbent tube.
3.4.2 Insert the sorbent tube into the rubber sleeve of the low flow holder or tube holder with the sorbent sections closer to the pump. Place the protective cover over the sorbent tube.
3.4.3 Attach the clip to the worker’s collar and the pump to the worker’s belt.
3.4.4 The sorbent tube should be placed in a vertical position during sampling.
3.4.5 Turn the pump on and note the start time and any other pertinent information.
3.5 After Sampling
3.5.1 At the end of the sampling period, turn the pump off and note the ending time. Remove the sorbent tube, seal the ends of the tube with the caps, and record pertinent sample information.
3.5.2 Perform post-calibration using the Electronic Bubble Meter. Obtain three readings, add the readings together, and divide by three for an average flow rate. Add the pre and post-calibration flow rates together and divide by two to obtain the average flow rate for the sampling period. Verify the readings have not varied by more than 5%. If readings vary more than 5% the sample should be voided.
3.5.3 Along with the sample tubes, submit field blanks from the same lot number as the sample tubes. Field blanks should be subjected to the same handling as the samples (break, seal, and transport) except that no air is drawn through them.
3.5.4 Pack the sample sorbent tubes, field blanks, and all pertinent information securely for shipment to the laboratory for analysis.
Note: You should check with the laboratory for specific information on the shipment of samples. Some gases and vapors are required to be refrigerated after collection and through shipment to the lab. Also, a chain of custody letter should be filled out and transported with the samples.