b. The interior of the blood storage refrigerator must be clean and adequately
lighted to facilitate the inspection of the blood, the refrigerator and the thermometers.
c. All refrigerators in which blood is stored should have recording thermometers
and must have audible and/or visual alarms to warn continuously of abnormal
temperatures. The sensor for the temperature-recording system should be in fluid (10 percent
glycerol in water) in a container with heat characteristics of the blood containers being
used and a volume no greater than the least donor blood or component in storage. The
sensor for the visual and audible alarm signals should be in the same container. The
alarm should be activated when the temperature falls outside the acceptable 1C to 6C
range. The electrical source for the alarm system should be separate from that of the
refrigerator, using either a continuously rechargeable battery or a separate electrical
house circuit. Finally, two mercury-type thermometers are recommended for monitoring
temperatures: 1 immersed with the sensors of the recorder and alarm system and 1 in a
similar container on the lowest shelf on which blood is stored. The temperatures of
these two thermometers must be 1C to 6C at all times. A daily check should show the
temperature of the thermometer at the top to be within 1C of that shown on the
automatic recorder. It is sufficient to record the temperatures from the two mercury
thermometers on the recorder chart when it is changed weekly. In large walk-in
refrigerators, it is recommended that such thermometer containers be placed in areas
determined to reflect the range of temperatures and efficiency of the cool air distribution.
d. Temperature charts from 7-day mechanical recording devices must be
changed weekly, dated inclusively, and labeled for proper identification of the
refrigerator. Any temperature variation from normal should be explained in writing on
the chart beside the tracing; but if the tracing is habitually a perfect circle, the recorder
may not be functioning properly. The person responsible for changing the charts should
sign them. All temperature records must be kept as part of the blood bank records a
minimum of 5 years.
e. Refrigerator thermometers and alarms should be checked periodically to
ascertain that they are functioning properly. The high temperature may be checked by
slowly adding warm water to the vessel in the refrigerator which contains the sensor of
the recording system and the calibrated thermometer. Stir constantly as the warm water
is added. Note the temperature on the thermometer and on the chart at which the alarm
sounds. The alarm should be activated just above 6C. The low temperature may be
checked by adding chipped ice slowly to the vessel containing the sensor of the alarm
system and the calibrated thermometer.
MD0845
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