C. Jackson, T. W. Hodge, D. H. Swingler, and A.
J. Smith, Some Aspects of Fires in Glove Boxes, AERE-R 3067, United Kingdom Atomic Energy Authority, October 1959.
attention. Some useful references include:
S. E. Smith, F. J. Hall, W. E. Holmes, and A. F. /7
Filters located outside a glove box require con- George, Protection Against Fire Hazards in the venient access for changing, and it is usually Design of Filtered Ventilation Systems of Radioac-
O R N L DWG. 6 9 - 0 7 7 5
EXHAUST CONNECTION PLASTIC BAGGING SLEEVES
SECURED AND SEALED AT F I L T E R END BY SEALING GLAND AT METAL EXHAUST DUCT END BY ELASTIC F L E X I B L E HOSE
METAL DUCT ON GROOVED RING
ADJUSTABLE CLAMP FOR SECURING ASSEMBLY
ENCLOSED HEPA F l L T
0
NORMAL POSITION
EXHAUST CONNECTION DISJOINTED, BAG SLEEVE EXTENDED AN0 HEAT SEALED, SLEEVE CUT IN SEALED PORTION TO PRESERVE SEAL OF BOTH ENDS SEALED SLEEVE STUB REMAINS ON END OF EXHAUST DUCT
0
EXHAUST CONNECTION SEVERED
CLOSED END I N L E T END OF F I L T E R IS DISJOINTED, H E A T
SEALED AND CUT FROM SYSTEM SIMILAR TO STEP 2. PRESERVING SEAL ON GLOVE BOX CONNECTION INSERT DIRTY F I L T E R IN ADDITIONAL PLASTIC BAG AND SEAL END FOR DISPOSAL AS CONTAMINATED WASTE
OPEN OPEN
END END
0
DIRTY F I L T E R SEPARATED FROM SYSTEM
I
C L E A N ENCLOSED H E P A F I L T E R PREPARED IN ADVANCE WITH PLASTIC BAGGING SLEEVES AND SEALING GLANDS ON F I L T E R CASING NIPPLES
NEW SLEEVE ON I N L E T SIDE OF F I L T E R I S AT- TACHEDTOGROOVEDRINGOVEROLDSLEEVE STUB WITH ELASTIC FASTENER, D E F L A T E SLEEVE
@
CLEAN FILTER I N L E T SEALED OVER SLEEVE STUBONGLOVE BOX
D L D S L E E V E S T U B R E M O V E O F R O M G L O V E BOX CONNECTION BY REVERSING CLOSED END POCKET IN SLEEVE AND USING AS GLOVE
VER POCKET WITH STUB IN END OF E T ENGAGE F I L T E R SEALING GLAND BOX CONNECTION STUB I S HEAT SEALED EEVE END, CUT AWAY (PRESERVING SEALS) DISCARDED AS CONTAMINATED WASTE
0
CLEAN F I L T E R SEALED TO GLOVE BOX EXHAUST CONNECTION
F O L D SLEEVES AND PROTECT FROMRUPTURE EXHAUST DUCT I S JOINED TO O U T L E T END OF CLEAR
F I L T E R SIMILAR TO STEP 5 PARTICULAR CAUTION WHERE TRAFFIC REQUIRES NECESSARY TO PREVENT LOOSE STUB FROM BEING
S U C K E D U P D U C T ALLOWBAGGINGTODEFLATEBEFORE CONNECTING DUCT SECURE ASSEMBLY WITH ADJUSTABLE CLAMP
0
EXHAUST CONNECTION SEALED TO FILTER, AIR FLOW RESUMED
NORMAL POSITION RESTORED WITH CLEAN F I L T E R I N PLACE
Fig. 7.20. Bagging technique for enclosed HEPA filter located outside the glove box.
5 3 r C O r . b f : T t N
Fig. 7.21. Enclosed HEPA filter being removed from exhaust stream outside glove box by bagging. Courtesy Oak Ridge National Laboratory.
tive and Toxic Process Buildings, AWRE 0-241 65, UKAEA, July 1965.
J. Young, Engineering Study of Radiological Fire Prevention at Lawrence Laboratory, Berkeley, California, UCRL-19465, Lawrence Radiation Laboratory, January 1970.
W. E. Domning and R. W. Woodward, Glovebox Fire Tests, RFP-1557, Rocky Flats Plant, Nov. 6,
1970.
L. R. Kelman, W. D. Wilkinson, A. B. Shuck, and R. G. Goertz, Safe Handling of Radioactive- Pyrophoric Materials, ANL-5509, Argonne National Laboratory, December 1955.
S. H. Pitts, Jr., “Factors Influencing the Ignition of Metallic Plutonium,” Nucl. Saf. 9(2), 112-19 (March-April 1968).
R. E. Felt, Burning and Extinguishing Char- acteristics of Plutonium Metal Fires, 1 SO-756, Richland, Wash. , August 1967.
H . V. Rhude, “Fire and Explosion Tests of Plutonium Glove Boxes,” p p . 305-11 in Proc. Hot Lab. Equip. Conf. lo th , Washington, D.C., Nov.
26-28, 1962.
A. J . Hill, Jr., Fire Prevention and Proteetion in Hot Cells and Canyons, DP-1242, Savannah River Laboratory, April 1971.
H . A. Lee, Guide to Fire Protection in Caves, Canyons, and Hot Cells, ARH-3020, Richland, Wash., July 1974.
NFPA 801, Recommended Fire Protection Prac- tice f o r Facilities Handling Radioactive Materials, National Fire Protection Association, Boston, 1970.
R. E. Giebel and R. L. Riegel, Drybox Gloves-Evaluation and Procurement, RFP- 1286, Rocky Flats Plant, June 23, 1971.
P. E. Johnson, Evaluation of Improved Fire Resistant Glove Materials f o r Gloveboxes, USAEC
179
Report TID-25086, Factory Mutual Research Corp., Boston, 1969.
C. W. Jacoby, Glovebox Window Materials, RFP- 1424, Rocky Flats Plant, Mar. 13, 1970.
Glovebox Window Materials, USAEC Report TID-24896, Factory Mutual Research Corp., Boston, 1969.
The task of fire and explosion protection can be divided into prevention, detection, and suppression.
These areas are discussed below as they apply to glove box operations and in Chap. 9.
Protection. Fire prevention in glove boxes is mainly accomplished by the following methods:
1.
2.
3.
4.
5.
6.
7
Using nonflammable materials in construc- Gloves and windows have received the most attention, since they are the most necessary and vulnerable parts of the glove box.
Strict adherence to acceptable housekeeping practices.
Avoiding the use of flammable materials within the box wherever possible and limiting the amount of flammables to the minimum re- quired for immediate use when no suitable nonhazardous substance can be substituted.
Using containers for flammable substances that are as safe as can be found for the planned operation.
Maintaining a current in-box material inven- tory and not using the box for storage. Boxes usually are inappropriate for storage, especially for chemicals.
Establishing a safer, nonoperative box con- figuration and periodically checking to make sure that nonoperating boxes are in safe 'condi- tion. Precautions include isolating boxes by closing fire stops, checking through-flow, checking port covers, disconnecting electrical equipment, and removing corrosives.
Designing the box with downdraft ventilation (high air inlet, low outlet), to inhibit combus- tion while still purging the box.
Providing a protective atmosphere (Sect. 7.5.2).
This measure was listed last because those preceding it are applicable to all glove boxes, whereas inerting is used only when there is too much risk involved in operating without a protective atmosphere. Assessing the degree of tion. 1,21839
risk involved in an operation is often a subjec- tive evaluation.
Detection. A glove box fire detection system is recommended when there is high risk of fire. If flammable solvents, coolants, packaging materials, etc., must be present during operation and especially in unattended boxes, a heat detector should be located within the box. Regulatory Guide 3. 1216 calls for heat detectors and combustible-gas or vapor- detection meters on glove boxes wherever fire or explosion hazards exist.
Fire detectors are required in plutonium glove boxes. l 7 A description of currently available detec- tors is given in the Factory Mutual safe practice guide.' Report DP-1242" contains a useful section on evaluating detectors.
Suppression. Since a fire within a glove box may be of paper, chemical, electrical, or pyrophoric metal origin, there is no single suppression method that is best for all glove boxes. Halon-1301" is an effective general extinguishing agent; it is better than carbon dioxide2" on chemical and electrical fires but ineffec- tive against pyrophoric metal fires;" and it decom- poses above 750°F. The use of carbon microspheres for extinguishing metal fires is discussed in Sect.
9.5.4. The complete exclusion of oxygen with rapid heat removal to below its ignition temperature ( 5 O O O C ) is effective for extinguishing plutonium fires. '
There is no assurance that filters will remain functional during and following exposure to fire, smoke, o r burning debris. The temperature reached during a fire, the quantity and density of smoke released, and the duration of the fire determine the destructive effects on prefilters and HEPA filters.
HEPA filters can withstand 750" F temperatures for periods up to 10 min but should not be subjected to indefinite exposure to temperatures higher than 275°F (Tables 3.4 and 3.5). Longer filter life and more reliable service can be obtained when normal operating temperatures are below 200" F and high temperature extremes are avoided.
The selection and arrangement of HEPA filters on, in, or near glove boxes and similar enclosures are limited by the type of fire control equipment used, because HEPA filters and most prefilters are not compatible with all types of fire extinguishing systems. Dry chemical extinguishers employ finely divided solids that can clog filters. Ideally, the
selectedto blanket the fire zone effectively without becoming airborne.
When large amounts of carbon dioxide (C02) are released from a cylinder, moisture in the glove box atmosphere may form ice crystals that can clog filters after only a few minutes of operation. Should this happen, introduction of more C02 is likely to overpressurize or perhaps rupture the box. Carbon dioxide is a poor fire extinguishing agent for glove boxes because of its tendency to clog exhaust filters, reduce airflow, and obscure vision when moisture is present.
When foaming agents or spray droplets from fire extinguishing systems reach a filter, it is quickly clogged if free moisture cannot be evaporated into the air passing through the filter. This limits the use of foam generators and water fogs to ventilation systems where emergency devices are actuated and controlled manually, or where continuous airflow through the filter (or filters) during an emergency is not required. The standard for high expansion foam systems is NFPA llA,22 and for synthetic foams, NFPA i i ~ . ~ ~