3.1 A calibrated personal sampling pump whose flow can be determined within ±5 percent at the recommended flow rate. 3.2. Charcoal tubes: Glass with both ends flame sealed, 7 cm long with a 6-mm O.D. and a 4-mm I.D., containing 2 sections of 20/40 mesh activated charcoal separated by a 2-mm portion of urethane foam.