Page:NIOSH Manual of Analytical Methods - 6601.pdf/2

 OXYGEN: METHOD 6601, Issue 2, dated 15 August 1994 - Page 2 of 3 REAGENTS: 1. 2.

EQUIPMENT:

Fresh air or 20.9% O 2, 79.1% N 2 in compressed gas cylinder.* 16% O 2, 84% N 2 in compressed gas cylinder for calibration.*



See SPECIAL PRECAUTIONS.

1. Oxygen monitor with electrochemical sensor with the following performance specifications: linear response between 15 and 21% O 2 in nitrogen; span and zero drift ≤0.2% O 2 for 8 h; response time ≤0.5 min for a 1% change in oxygen concentration. 2. Air pump, 0.2 to 2 L/min, and plastic tubing to sample remote locations (optional). 3. Sample bags to collect samples (optional). 4. Sensor cap with inlet and outlet fittings to calibrate from compressed standard cylinders in contaminated atmospheres. 5. Air line adaptor for sampling oxygen-enriched air.

SPECIAL PRECAUTIONS: Shipments of compressed calibration gases must comply with 49 CFR 1992 regulations.

SAMPLING AND MEASUREMENT: 1.

2.

Start monitor as manufacturer recommends. Allow sufficient warm up/equilibration time if monitor has been in a different environment. If a remote sensor is used in an area different from the monitor electronics, allow extra time to reach thermal equilibrium. NOTE: Instrument warm-up time is typically 10 min or less, but may increase to as long as 1 h if sampled atmosphere varies 5 °C or more from present ambient temperature. Select one of the following sampling modes as appropriate: a. Ambient air or oxygen-deficient air: (1) Place monitor in atmosphere to be analyzed. Allow to equilibrate. (2) Record % O 2. Read and record frequently. Observe any downward trends in % O 2 levels. If a concentration of 19.5% O 2 is approached, ventilate with fresh air if possible. WARNING: EVACUATE THE AREA WHEN THE O 2 CONCENTRATION FALLS BELOW 19.5% [3]. b. Oxygen-enriched air: (1) Place sensor in air line adaptor. Allow to equilibrate. NOTE: If line is pressurized, bleed off a stream to the sensor at atmospheric pressure in order to not pressurize the sensor. (2) Record % O 2.

CALIBRATION AND QUALITY CONTROL: 3.

4. 5.

Perform on-site calibration at 20.9% O 2 several times each shift by exposing sensor to fresh air or to standard tank air. Replace sensor cell when the instrument can no longer be adjusted to read 20.9% O 2 in fresh air. WARNING: DO NOT PRESSURIZE THE SENSOR WITH CYLINDER MIXTURES AS THIS WILL CAUSE HIGH READINGS AND COULD DO IRREPARABLE DAMAGE TO THE SENSOR CELL. Perform down-scale calibration by exposing sensor to 16 to 19% O 2 in N 2 at least once per day. Check for alarm function (if included) by exposing to 16 to 19% O 2 in N 2 from a cylinder or by blowing self-exhaled breath directly onto the sensor. Following manufacturer's instructions for this procedure, adjust readout meter to agree with the calibration standard.

NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94