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Use of Portable HEPA Filtered Ventilation Units

Use of Portable HEPA Filtered Ventilation Units. HEPA Filtered Ventilation. Used to “capture” airborne particulate and confine its spread Workers need to understand the dynamics of how to capture particulate to be effective. REQUIREMENTS.

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Use of Portable HEPA Filtered Ventilation Units

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  1. Use of Portable HEPA Filtered Ventilation Units

  2. HEPA Filtered Ventilation • Used to “capture” airborne particulate and confine its spread • Workers need to understand the dynamics of how to capture particulate to be effective.

  3. REQUIREMENTS • Portable air-handling equipment used in CAs, HCAs, or ARAs should be equipped with HEPA filters • HEPA filters should meet the efficiency and construction requirements for HEPA filters

  4. REQUIREMENTS • Maximum flow rate of the device should not exceed the flow rate the HEPA filter was tested • Units should be aerosol tested before initial use, annually, and when opened.

  5. REQUIREMENTS • Uniquely marked and labeled • Controlled by RWP • Controlled to prevent Unauthorized Use

  6. REQUIREMENTS • Designed to ensure HEPA filter integrity under conditions of use, and • Designed to prevent unauthorized or accidental access to inner surfaces

  7. Characteristics of Portable Vent System • Need “Nuclear grade” equipment • Keep hose/duct length short with minimum bends. Route through low traffic areas. • Bends should have minimum bend radius of 2-2.5 times hose/duct diameter. Sharp bends are equivalent to adding more hose or duct equal to 6-8 times hose diameter.

  8. Characteristics of Portable Vent System • Install straight duct section of a least 6 equivalent duct diameters at a location where hose connects to fan housing • Hose/duct should be round, smooth-bore and free of obstructions • If dampers must be used, install midway in hose and secure with tamper-proof device

  9. Characteristics of Portable Vent System • Use “localized” or “capture” ventilation close to contamination source • Flow rate must be high enough to capture particulate and keep it in air stream • Position hose within one duct-diameter and modify the suction to pull air from the region where airborne particulate is being produced

  10. Flow Contours % of Velocity 100% 60% 30% 15% 7.5% % of Diameter • Velocity Contours • Circular hose inlet opening • % of opening velocity

  11. Capture Velocity • The air velocity at any point in front of a hood or hose/duct opening necessary to overcome opposing air currents and capture the contaminated particles at that point and cause them to flow into the ventilation system.

  12. Capture Velocity • Recommend minimum of 125-200 fpm at contamination source • In quiet air need 50-100 fpm • During grinding, need 500-2000 fpm to capture high velocity particles

  13. Face Velocity • Air velocity in feet per minute (fpm) at hood, hose or duct opening. • This velocity varies based on the size of the system, amount of hose or ducting, fittings, and other system losses due to the configuration.

  14. Minimum Duct Velocity • Minimum air velocity required to move particulates in the air stream. • Normally, this ranges from 1500-4500 fpm • This velocity depends on type and size of material, i.e., vapor, gas, fume, dust, debris, etc.

  15. Characteristics of Portable HEPA Vent System • Use funnel, scoop, or hood to improve capture • Force incoming air to pass through region that contains airborne particulate • Place vent suction at 90 to 180 degrees from worker on opposite side of source at one duct diameter or less

  16. Characteristics of Portable HEPA Vent System • System fitting should be tapered to reduce restrictions. Most units are not tapered to cut cost and save space. • Securely seal joints to avoid leaks and increase flow • Install demister when needed to remove liquid from damp air. Damp HEPA filters lose tensile strength.

  17. Characteristics of Portable HEPA Vent System • Locate system in a well-lighted and weather protected area • Ensure air discharged by the system does not disturb contamination or insulation. • If used for “hot work” use metal ducting and spark arrestor to remove sparks and prevent fire

  18. Air Flow Calculations • Air changes in the tent work section should provide a minimum of 7-12 air changes per hour or whatever the facility requires. Many facilities use 20 air changes per hour as the desired flow. • Air changes are determined by dividing the rated CFM of the vent system into the volume of the containment

  19. Air Flow Calculations • For Example: • Tent is 10’ x 12’ x 8 = 960 ft3 • Vent system is rated at 300 CFM • 960 ft3 x 60 min = 18.75 AC/hr • 300 CFM 1 hr

  20. Air Flow • If localized or capture ventilation is used, the important thing to consider is the amount and direction of flow at the contamination source and the worker’s breathing zone.

  21. In Summary • Get the hose/duct close, within one duct diameter • Install scoop, hood, or flange to force incoming air to pass through the contamination source • Smoke test prior to work and look at worker’s body position • Check blower discharge

  22. Vent & Balance • When system is set up, call Vent & Balance at 373-2746 or 373-9275 to arrange for aerosol testing

  23. Resources You Need • Industrial Ventilation Manual • - Purchase from American Conference of Governmental Hygienists at (513) 742-2020 or Website http://www.acgih.org/store/. Cost is about $100.00 and they take a P-Card. They also sell another book on “Ventilation for Contaminant Control”.

  24. Use of HEPA Filtered Vacuum Cleaners

  25. CAUTION • Improper use of vacuum cleaners may result in the generation or airborne radioactivity, loose surface contamination, or high dose rates

  26. Requirements for Using Vacuums for Rad Work • Should be equipped with HEPA filters that meet special efficiency and construction requirements • Nuclear Safety Review should be performed & documented before use with fissile material • The maximum flow rate of the vacuum should not exceed the flow rate used to test the HEPA filter

  27. HEPA Filtered Vacuums • HEPA filters remove debris from the air stream, including radioactive particles • Vacuum cleaners collect most of the debris before it reaches the filter in disposable bags or containers • Some are designed for collecting wet materials and some are explosion-proof

  28. Requirements for Using Vacuums for Rad Work Leak test prior to use, annually, and when opened*. Also when dropped, jarred, or exposed to water vapors, chemicals, or high temperatures. • * If the vacuum is designed to be serviced without effecting the HEPA filter seal, it does not require retesting.

  29. Requirements for Using Vacuums for Rad Work • Vacuum cleaners should be: • 1. Uniquely marked and labeled • 2. Controlled by an RWP, • 3. Controlled to prevent unauthorized use,

  30. Requirements for Using Vacuums for Rad Work • 4. Designed to ensure HEPA filter integrity under conditions of use, and • 5. Designed to prevent unauthorized or accidental access to the inner surfaces of the vacuum cleaner

  31. Requirements for Using Vacuums for Rad Work • Radiation and contamination surveys should be performed periodically while in use and labels updated. • The frequency of radiation surveys should depend on the specific use of the vacuum • Air samples should be taken if the unit is used in a High Contamination Area

  32. Requirements for Using Vacuums for Rad Work • Surveys should be performed before, during and at the completion of work that has the potential for causing changes in levels of radiation and radioactivity. Recommend marking survey points on the vacuum cleaner • Survey frequencies should be based on potential conditions, probability of change and area occupancy factors.

  33. Guidelines • Contact line organization for vacuum • Verify unit has been tested within last year (365 days) • Ensure any security seals are intact • Inspect hoses and vacuum for integrity

  34. Guidelines • If vacuum is contaminated, check bagging on hose end and labels • Position vacuum close to work and route hose through low traffic areas • Keep hose straight with gradual bends

  35. Guidelines • Securely clamp or tape hose connections • Secure vacuum in upright position • If wet/dry unit is used, verify any drain valves are shut

  36. Guidelines • If used for ventilation, position hose within one duct diameter so airborne particles are drawn away from worker. On shrouded tooling, the hose is connected to the tool • If used to remove debris, don’t vacuum large particles or materials that will plug the hose.

  37. Guidelines • Consider installing collector to remove highly radioactive debris before it reaches the vacuum • In addition, a filter could be installed in the vacuum cleaner hose so the HEPA filter in the vacuum cleaner stays low rad.

  38. Guidelines • If collecting liquids or damp debris ensure vacuum cleaner is a wet/dry unit • Ensure procedures are established so the unit is not overfilled and the workers understand how the unit will be used and emptied

  39. Guidelines • If used to collect low-level rad waste, don’t mix with “TRU” or “Mixed Waste” • If Vent & Balance sticker is torn or integrity seals are broken, the unit must be removed from service and retested prior to use

  40. Precautions • Don’t run electrical vacuums for long periods or they may overheat and catch fire • Don’t use an electric vacuum cleaner to remove explosive gases. Use an explosion-proof unit and get approval from safety

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