EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass thermometers In Reply Refer To: November 22, 1993 Mail Stop 412 OFFICE OF WATER QUALITY TECHNICAL MEMORANDUM NO. 94.02 Subject: EQUIPMENT--Discontinuance of field use of mercury liquid-in-glass thermometers The purpose of this memorandum is to announce that mercury liquid-in-glass thermometers are no longer to be used in the field. Alternatives are thermistor thermometers, digital hand-held thermometers, and red safety liquid- in-glass (alcohol) thermometers. The reasons for this change are to prevent contamination of samples, vehicles, and the environment resulting from broken mercury thermometers and to limit exposure of field personnel to mercury vapors resulting from spills. Mercury-filled NIST-calibrated thermometers can be used to calibrate thermometers in the laboratory only. The NIST thermometers should not be taken into the field. Water-quality monitors can be calibrated using lab-calibrated thermometers. The Hydrologic Instrumentation Facility (HIF) recently tested the Cole-Parmer Model No. 90201-10 hand-held thermometer in hopes that it could provide an alternative to more expensive thermistor thermometers. The test results (see Attachment 1) show that the thermometer meets the manufacturer's specification for accuracy of +/- 0.2 degrees Celsius (C) in the range tested, and that the unit performs well concerning environmental effects on accuracy and tolerance towards temperature change. Please note the recommendations regarding the care and handling of this thermometer. The Cole-Parmer thermometers can be purchased from HIF for $60, or individually from the company. Other liquid-in-glass or thermistor thermometers with accuracies of at least +/- 0.5 C can also be used to measure temperatures in the field. Temperature measurements made with multi-parameter units such as the Hydrolab are also acceptable. Thermistors on other meters, such as dissolved-oxygen meters, must be calibrated and checked for accuracy before being used. As with other field meters, all thermometer calibrations should be recorded in a dedicated log book. Read Quality of Water Branch Technical Memorandum No. 79.16 for information on quality assurance of temperature measurements. Data-quality objectives should be taken into consideration when selecting a thermometer. Current basic-data requirements are to report air and water temperatures to the nearest 0.5 C. The liquid-in-glass pocket thermometers generally have 1 degree divisions and, therefore, cannot be read as accurately as a digital or thermistor thermometer, but they can be read to the nearest 0.5 C. If the need arises, the HIF will test additional digital thermometers as requested by the Office of Water Quality or through the HIF Instrument Test Program. David A. Rickert Chief, Office of Water Quality This memorandum does not supersede any other Office of Water Quality Technical Memorandum. Key Words: Temperature, Thermometers, Thermistors, Mercury Distribution: A, B, S, FO, PO, AH ATTACHMENT 1 (Modified from WRD Instrument News, Issue No. 62, September 1993) ATTENTION--A REPLACEMENT FOR THE MERCURY THERMOMETER The HIF has completed testing and evaluating the Cole-Parmer Digital Thermometer, Model 90201-10 to determine whether it can be used as an alternative to the mercury thermometer. The following test report indicates that this digital thermometer meets the accuracy specifications, performs well within a specified range of environmental conditions, and is tolerant of temperature change within a specified range. Please read the conclusions and recommendations carefully. THE DIGITAL THERMOMETER UNIT SHOULD BE HANDLED WITH CARE. TEST AND EVALUATION REPORT Cole-Parmer Digital Thermometer Model 90201-10 General Discussion Two Cole-Parmer model 90201-10 digital thermometers were evaluated. Three tests were used in the evaluation. 1. Accuracy. -- Both units were tested in water baths at various temperatures between 5 and 100 C); a NIST-traceable thermometer was used as a reference. The differences between temperature readings from both the NIST-traceable thermometer and readings from both units are generally equal to or less than +/- 0.2 C (table 1). Both Cole-Parmer units met the manufacturer's specifications. 2. Environmental Effects On Accuracy. -- The ambient temperature is commonly different from the water temperature. Checking the performance of the units under these conditions is essential for the evaluation. The units were placed in an environmental chamber in which both temperature and humidity were controlled; the temperature sensors were placed outside the chamber in the water bath. Water temperatures were measured with both Cole-Parmer units. Measurements made with a NIST-traceable thermometer were used as reference Both units performed well (table 2). 3. Tolerance Toward Temperature Change. -- Both units, including the temperature sensors, were placed in an environmental chamber for 50 hours. The chamber was set in 5-hour cycles with temperature changes from 5 to 35 to 5 C; humidity was kept between 40 and 50 percent. After 10 cycles, the units were taken out of the chamber, and function tests were performed at 5, 15, and 25 C. Both units functioned well (table 2). Conclusions and Recommendations Both Cole-Parmer units met the manufacturer's specification for accuracy (+/- 0.2 C) in the range tested. The outer package of the unit is not physically strong and users should exercise special care in handling the unit. The plate holding the battery becomes detached and breaks off easily. Users should verify that the batteries are making good contact. The unit itself cannot take freezing temperatures and is not waterproof-- HANDLE WITH CARE. TABLE 1.--Water bath temperatures (C) as measured by a reference thermometer and two Cole-Parmer model 90201-10 digital thermometers in thermometer accuracy test [C, degrees C] ----------------------------------------------------------------- BATH NIST-Traceable Cole-Parmer Cole-Parmer Thermometer Unit 1 Unit 2 ----------------------------------------------------------------- 0.0 0.05 0.2 0.4 5.0 5.10 5.1 5.3 10.0 10.10 10.0 10.2 15.0 15.10 15.0 15.2 20.0 20.00 19.9 20.1 25.0 25.00 24.9 25.1 30.0 30.05 30.0 30.2 35.0 35.05 34.9 35.2 50.0 50.00 50.1 50.3 75.5 75.50 75.5 75.8 98.4 98.40 98.7 98.6 ----------------------------------------------------------------- TABLE 2.--Water bath temperatures (C) as measured by a reference thermometer and two Cole-Parmer model 90201-10 digital thermometers, whose meters were placed in an environmental chamber at a temperature different from that of the water bath, in thermometer accuracy test [C, degrees C] ------------------------------------------------------------------------ Meter in | Sensor environmental | in water bath (degrees C) chamber | -----------------|------------------------------------------------------ | NIST-Traceable Cole-Parmer Cole-Parmer Temperature (C) | Thermometer Unit 1 UNIT 2 -----------------|------------------------------------------------------ 5.0 | 0.0 0.1 0.3 | 5.1 5.1 5.3 | 15.0 14.9 15.1 | 25.0 24.9 25.1 | 34.9 34.8 35.1 -----------------|----------------------------------------------------- 15.0 | 0.0 0.2 0.4 | 5.1 5.0 5.3 | 15.0 14.9 15.1 | 24.9 24.8 25.0 | 34.9 34.6 34.9 -----------------|------------------------------------------------------ 25.0 | 0.1 0.2 0.4 | 5.1 5.2 5.4 | 15.0 14.9 15.2 | 25.0 25.0 25.2 | 35.0 34.8 35.0 -----------------|------------------------------------------------------ 35.0 | 0.2 0.3 0.5 | 5.0 5.0 5.2 | 15.0 14.9 15.1 | 25.0 24.9 25.0 | 35.0 34.8 35.0 ----------------|------------------------------------------------------ Note: The humidity was kept between 40 and 50 percent. PURCHASING The HIF has placed an order for 50 units to be sold at $60 each. The price includes HIF overhead. The units are not on GSA schedule, but WRD offices can buy them if they keep their order under $300. The normal price of the unit is $39.50. HIF will alert the field when its units are available. FOR FURTHER INFORMATION For further explanation/discussion, contact Doreen Tai (DYTAI) at 601-688-1518. Vito J. Latkovich Chief, Hydrologic Instrumentation Facility