USGS Ohio Water Science Center

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Ohio Water Microbiology Lab

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Ohio Water Science Center

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Quality Assurance/Quality Control Manual: Ohio Water Microbiology Laboratory


hoodThe OWML has four types of hoods—two biosafety cabinets (Hoods 1 and 5), a laminar-flow hood (Hood 2), a hazardous-waste fume hood (hood 3), and two PCR workstations (Hoods 4 and 6).

  • The operation of all hoods (except for the PCR workstations) are checked and certified by a qualified inspector annually and recorded in the LIMS.

The biosafety and laminar flow hoods have magnehelic pressure gauges (MAG) that are used to monitor operation of the hoods. Effectively running hoods will have pressure readings at levels approximately equal to the annually recorded MAG level in the calibration report. A significant increase in pressure indicates that the filters are dirty whereas a significant decrease in pressure indicates an electrical problem.

The biosafety cabinets, laminar-flow hood, and PCR workstation (Hoods 1, 5, 2, and 4) must be free from contamination.

  • The working surfaces of the biosafety cabinets, the laminar-flow hood and the PCR workstations (Hoods 1, 5, 2, 4, and 6) are wiped down with a surface disinfectant. The gold standard for hood disinfection is to wipe down the working surface with 10% household bleach and then wipe down with ethanol, methanol, or Conflikt before and after use. Each of these hoods should be more thoroughly disinfected quarterly. Quarterly disinfection requires that all surfaces inside the working area are treated as described above, including underneath the removable working surface of the biosafety cabinets. Quarterly internal cleaning of the hoods are recorded in the LIMS.
  • The biosafety cabinets and PCR workstations (Hoods 1, 5, 4, and 6) have ultraviolet (UV) bulbs for additional germicidal purposes. When possible, UV lights are to be turned on in the hoods for up to 15 minutes before and after hood use (longer exposure can begin to any degrade plastics contained in the hood). The UV lights in the biosafety cabinets and PCR workstations are cleaned quarterly by wiping the bulbs with a soft cloth and methanol or ethanol. Cleaning dates are recorded in the LIMS. A bulb that is dull in the center needs to be replaced. Record the bulb change in the LIMS.
  • Biannually, nonselective media plates are exposed to airflow in the laminar-flow hood, the biosafety cabinets, and PCR workstations for 1 hour (Hoods 1, 5, 2, 4, and 6). The plates are incubated at 35oC for 24 hours and examined for contamination. The results are record in the LIMS. If contamination (growth on nonselective media) is observed, whole-hood disinfection will be done as described above for the quarterly treatment.

The hazardous-waste fume hood (Hood 3) must be checked to ensure that it is operating properly.

  • Check the operation of the hazardous-waste fume hood (Hood 3) quarterly by use of fume cartridges and record results in the LIMS.
  • A light-weight lab wipe (single-ply) is taped to the outside of the hood sash as a quick check for proper airflow.

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