OXYGEN: METHOD 6601, Issue 2, dated 15 August 1994 - Page 3 of 3 6.
Practice routine instrument maintenance. a. Check sensor cell diffusion barrier for dirt and moisture. Clean with a soft cloth or tissue if needed. b. Replace sensor cell every six to nine months with average use. NOTE 1: Store cell in nitrogen when not in use to prolong life. NOTE 2: Some models use non-disposable, user-rechargeable sensors which require recharging every two to four weeks. c. Check batteries and replace when needed. NOTE: Battery life is two to six months for replaceable battery models. Some are equipped with nickel-cadmium batteries which require periodic recharging. Most operate at least 16 hrs without recharging. Some units have low-battery indicators.
EVALUATION OF METHOD: Oxygen monitors have been used successfully in numerous industries for pre-entry checks of areas where oxygen levels may be low and for continuous monitoring during the time workers occupy these areas [3]. They have also been used in hospitals for monitoring oxygen levels in oxygen-enriched atmospheres supplied for medical purposes. This method has undergone extensive laboratory evaluation for use in oxygen-deficient atmospheres and has been shown to be stable and reproducible [1]. The relative standard deviation, S r, for 15 different instruments monitoring the same atmosphere (under laboratory conditions) was 0.52% for over 100 readings over an 8-h period. The relative standard deviation, S r, for 18 different instruments monitoring the same atmosphere in field situations was 1.22% for 126 readings taken over a two-day testing period with calibration at the beginning of each day [1].
REFERENCES: [1] [2] [3]
Woodfin, W. J. and M. L. Woebkenberg. An Evaluation of Portable Direct-Reading Oxygen Deficiency Monitors (NIOSH, unpublished, 1984). Katz, Morris, Ph.D., Ed. Methods of Air Sampling and Analysis (Second Edition), Library of Congress Cat. No. 77-6876, American Public Health Association (1977). Criteria for a Recommended Standard...Working in Confined Spaces, U.S. Department of Health, Education, and Welfare, Publ. (NIOSH) 80-106 (1979).
METHOD WRITTEN BY: William J. Woodfin and Mary Lynn Woebkenberg, NIOSH/DPSE.
NIOSH Manual of Analytical Methods (NMAM), Fourth Edition, 8/15/94
