Summary

Laboratory hoods must be tested to verify proper operation and validate performance over the range of expected operating conditions.

  • As Manufactured tests to evaluate design of the hood itself, regardless of where it is installed
  • As Installed tests verify performance once the hood is installed in the lab to assess how it interacts with other components of the ventilation system
  • As Used tests verify continued performance as the ventilation system and hood age and to capture and repair operation of the equipment outside of acceptable ranges
  • Training and certifications of the technicians performing these tests
intro testing group graphic
Group led by Tom Smith
Exposure Controls Technology
tom smithTom Smith

Laboratory hoods must be tested to verify proper operation and validate their performance over the range of expected operating conditions. The tests can be conducted as manufactured to evaluate the design of the hood, as installed to evaluate the impact of the laboratory environment on hood performance, and as used to evaluate the impact of the experimental apparatus on hood performance.  The challenge tests generally include measurement of face velocity, cross draft velocity, VAV controls response and stability, visualization of airflow patterns and tracer gas containment tests.  The hoods can also be subject to various simulations and dynamic challenges such as equipment loading, pedestrian walk-by, door opening/closing and thermal stratification.  This section will review the various test methods and provide guidance on specifying and conducting laboratory hood tests pre-purchase, following installation and during routine tests.

Questions to be addressed include:

  1. What tests are required to evaluate the hood as manufactured prior to purchase and installation?
  2. What information should be provided to those selecting hoods and designing the systems?
  3. What tests are required to conduct during commissioning to validate operation and verify performance prior to occupancy and hood use?
  4. What tests are appropriate for routine testing and how often should tests be conducted?
  5. What is the difference between As Installed, As Used and routine maintenance tests?
  6. Should routine tests include more than face velocity tests, particularly for complex VAV systems?
  7. If hood performance can be affected by room conditions, should room conditions be documented and tested during commissioning and routine tests?
  8. What test data should be stored for future use?
  9. How do you calibrate and verify proper operation of hood monitors?
  10. Should hoods be tested as found or under worst case test scenarios (i.e. all hoods open in a laboratory at maximum flow)?
  11. Should hoods be tested while simulating hood loading or walk-bys?
  12. Should hoods be tested while modulating room temperature and supply diffuser discharge temperatures from full heating to full cooling and when?
  13. Should a performance envelope be developed for all laboratory hoods and provided by the manufacturer to determine the required operating specifications?
  14. How does the presence of occupancy sensors in the control system impact testing strategies?
  15. How much training, experience or certification is required to qualify people conducting tests?
  16. Should hood testers be certified and, if so, by whom?

testing positions

 Discussion Notes from Small Group Participants

The group discussed a number of topics related to Laboratory Hood Test Methods:

  • Key Questions to Consider:
    1. What are the objectives of testing?
    2. When to test?
    3. What tests should be conducted?
    4. Test conditions and challenges
    5. Who should conduct tests (what qualifications should they have)?
    6. Interpretation of results: Pass/Fail: uniformity of reporting;
    7. An Important Factor in answering questions is identifying testing that allows a Reasonable Cost for this process
  • Objectives
    1. Containment of what – chemicals, particles, heat, other factors?
    2. Normally this is in terms of chemical/airborne contaminants
    3. Contain, capture, exhaust
    4. Airflow direction / patterns
    5. Dilution of the contaminants is the ultimate strategy in meeting the Key Goal of Protecting the user from over exposure

test results

  • Operating Conditions that affect containment
    1. Face velocity – magnitude, distribution, turbulence, flow
    2. Sash position, configurations, area, permutations/combinations
    3. Loading – large pieces of equipment, piping lattices
    4. Cross drafts from room air movement
    5. Heat load in the hood
    6. Flow stability, response time after perturbations, total volume flow changes
    7. The Operator: Body Zone is defined by the height and size of body as well as its movement
    8. Differential pressure
  • As Manufactured testing can provide a Performance Envelope
  • As Installed means a Commissioning Test in place in the lab
  • What does Representative Sample mean in practice?

specifying tests

  • What tests are appropriate to implement routinely?
    • Routine testing: Can As Used testing be used as a Proxy?
    • Defining As Used can be a complicated process in some labs
hood tests and frequency
As Installed Testing RequirementsAs Used Testing Requirements

Diagrams from EPA Performance Requirements for Lab Fume Hoods_2-26-09-rev

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