Masonry Magazine April 1975 Page. 15
COMBUSTIBLE FRAMING OR FACING
Conditions of Acceptance. The test procedure for walls supporting combustible framing or facing is essentially the same as for other walls. However, no hose stream test is required. The test is successful and a fire resistance period may be assigned if:
1. The protection withstands the test and no combustible members ignite.
2. And, the contact-surface temperature of combustible members does not increase more than 250 F (121 C). For members closely embedded on three sides in masonry, concrete, etc., the permissible temperature rise is 325 F (163 C).
AMOUNT OF COMBUSTIBLES RELATED TO SEVERITY OF FIRE
Burn-out tests conducted at the National Bureau of Standards, which were performed in fireproof structures with various concentrations of combustibles having calorific values in the range of wood and paper (7000 to 8000 Btu per lb) and assembled to represent building occupancies, indicate that the relation between the amount of combustibles and the fire severity is approximately as given in Table 1 which is reproduced from National Bureau of Standards Report, BMS92, Fire-Resistance Classifications of Building Constructions, October 1942.
TABLE 1
Relation of Amount of Combustibles to Fire Severity
| Average Weight of Combustibles, Ib per sq ft of floor area | Fire Severity, hr | Average Weight of Combustibles, Ib per sq ft of floor area | Fire Severity, hr |
|---|---|---|---|
| 5 | ½ | 30 | 3 |
| 7½ | ¾ | 40 | 4½ |
| 10 | 1 | 50 | 6 |
| 15 | 1½ | 60 | 7½ |
| 20 | 2 | | |
COMBUSTIBLE CONTENTS IN BUILDINGS
In 1947, the Office of Technical Services of the Department of Commerce sponsored an investigation of the weights of combustible contents in various occupancies. This survey was made by the Public Buildings Administration under the supervision of the National Bureau of Standards and the results are reported in National Bureau of Standards Report, BMS149, Combustible Contents in Buildings, published July 1957. Regarding the weights of combustibles reported, the report states:
"Only the weights of combustible contents, finished flooring, interior finish, and trim are included in the weight totals. No combustible structural elements are included because they are a part of the building itself and not of the contents.
"In general, the amounts of combustibles were obtained by weighing combustible furniture, equipment, goods, and other combustible contents in sufficient quantity to enable the total weight of such material within each area to be computed. The weight of any combustible flooring material, showcases, partitions, door and window trim, and built-in fixtures which could not be weighed, was estimated from the thickness and area. All of the weights were converted to equivalent weights of combustibles having a calorific value in the range of wood and paper."
Table 2 gives average combustible contents of various occupancies as included in the authors' summary of BMS149.
TABLE 2
Average Combustible Contents of Occupancies
| Occupancy | Combustible Loading Ib per sq ft | Remarks |
|---|---|---|
| Residential | 10 | A reasonable value, including storage rooms |
| Hospitals Patients rooms, dormitories, waiting rooms, corridors, kitchens and dining rooms | 0.810 3.9 2.910 86 | Maximum in areas for treatment, surgery and clinics = 21.6 lb per sq ft |
| Administrative and offices Service areas, store rooms, laundries, etc. | 0.5 to 13.1 | |
| Schools | 15 | Library stackrooms, store rooms and offices, representing a small percentage of total area, had higher combustible loads. |
| Mercantile Establishments Department stores | Not over 20 | |
| Manufacturing Establishments Clothing factories Printing establishments Offices | 20 30 20 | |
In order to determine the total fuel content or total conflagration hazard represented by a building and its contents, the fire hazard represented by the combustible materials incorporated in the structure itself must be added to the combustibles incident to the occupancy of the building.
FIRE RESISTANCE
The fire resistance ratings of walls and partitions are usually less than ultimate fire resistance periods as determined by test, since most building code requirements are in multiples of 1 hr with a 4-hr maximum. Table 3 gives ultimate fire resistance periods for solid
TABLE 3*
Ultimate Fire Resistance Periods for Loadbearing
Clay and Shale Brick Walls
| Nominal Wall Thickness, In. | Wall Type | Ultimate Fire Resistance Period in Hours |
|---|---|---|
| | | Incombustible Members Framed Into Wall or No Framed-in Members | Combustible Members Framed Into Wall |
| | | No Plaster | Plaster on One Side | Plaster on Two Sides | No Plaster | Plaster on Exposed Side |
| 4 | Solid | 1¼ | 1½ | 2½ | | |
| 8 | Solid | 5 | 6 | 7 | 2 | 2½ |
| 12 | Solid | 10 | 10 | 12 | 8 | 9 |
| 12 | Solid | 12 | 13 | 15 | | |
| 9 to 10 | Cavity | 5 | 6 | 7 | 2 | 2½ |
Adapted from BMS32, Reference 7.
"To achieve these ratings, each plastered wall face must have at least ts-in, 13 gypsum
sand plaster.
Based on load failure
Based on temperature rise (for non-loadbearing walls).