Bag-in bag-out housing
A sealed filter housing whose loaded filter is removed into a plastic bag attached to the access port and replaced through a new bag, so the filter and the housing interior are never open to the room. It is used where exhaust filters collect hazardous or radioactive material.
Also called BIBO housing, bag-in/bag-out, safe-change filter housing
What is a bag-in bag-out filter housing?
A bag-in bag-out housing is a containment filter housing whose contaminated filter is changed through a sealed plastic bag, so nobody is exposed to the filter or the housing interior. The DOE handbook calls for shutoff dampers on both sides so the housing can be isolated during the change.
Bag-in bag-out housing: how it works
A bag sealed to a collar around the access port lets a technician reach the filter through the plastic, release its clamp, and pull it into the bag. The bag is closed and cut between two seals, leaving a sealed stub on the port, and a new filter goes in through a new bag that pushes the old stub out. Dampers upstream and downstream isolate the housing so the bag does not balloon or collapse when the door opens.
Where you meet the term
- In the exhaust from gloveboxes, hot cells, and radiological laboratories.
- In containment laboratory and hazardous material exhaust systems where a loaded filter must not be handled open.
- In a filter housing specification, beside requirements for in-place test sections and isolation dampers.
How to check it
- Confirm the change procedure is available. The housing's written change procedure, including damper isolation and the bag sealing steps, should be in the maintenance team's hands before any change is scheduled. Owner check
- Leak test the new filter and the housing. After a change, a technician performs the in-place leak test on the new filter and checks the housing cover and port seals. Technician
Bag-in bag-out housing: what it is not
- A bag-in bag-out housing does not make a filter change safe without isolation. With the dampers open, the pressure difference moves the bag and can breach it.
- The bag does not replace testing. The new filter still needs an in-place leak test once it is seated.
Bag-in bag-out housing questions
Why is a bag-in bag-out housing kept slightly negative during a change?
The DOE handbook notes that a slight negative pressure in the housing, about 0.25 to 0.5 inches of water gauge, helps ensure any leakage during the change runs inward into the housing rather than out into the room.
What sealing surface thickness does the DOE handbook recommend for housings?
At least 0.078 inch, which is No. 14 U.S. gauge sheet metal. A thinner or warped surface cannot hold a gasket seal evenly, so the handbook also calls for the surface to be seal-welded into the housing.
Can a bag-in bag-out housing hold more than one filter stage?
Yes. Housings range from a single small side-access filter to multistage units with a demister, a medium efficiency filter, two HEPA stages, and an adsorber, each stage reached through its own bagged port.
Where this definition comes from
Written from government guidance, standards body publication material held in the HVAC Bench evidence record. Where a document limits a definition to certain models, that limit is repeated here rather than generalised across a brand.
- DOE-HDBK-1169-2022, Handbook for use with DOE-STD-1269-2022, Air Cleaning Systems in DOE Nuclear FacilitiesDOE handbook replacing the 2003 Nuclear Air Cleaning Handbook: primary, secondary, and tertiary confinement zones with air flowing toward the more contaminated zone and pressure differentials that prevent backflow under upset conditions; a 100 feet per minute rule of thumb for capture velocity across a primary confinement breach; positive seals at secondary barrier penetrations; bag-in bag-out side-access housings with upstream and downstream shutoff dampers and provisions for in-place testing; parallel housings with inlet and outlet isolation dampers; a recommended 0.05 percent maximum leakage acceptance for in-place HEPA system tests under ASME AG-1 Appendix TA; backup power for fans, dampers, and controls where safety documentation requires it; and stack guidance of exit velocity at least 1.5 times wind velocity with 3,000 feet per minute recommended, noting that high velocity is no substitute for proper stack location.
- ASME AG-1, Code on Nuclear Air and Gas TreatmentRequirements for the performance, design, construction, acceptance testing, and quality assurance of individual components of nuclear safety-related air and gas treatment systems, including HEPA filters, housings, dampers, fans, and ductwork, with field testing in Section TA; the code covers components only and not functional system design or sizing.