Take a Look at Flame Spread And Life Safety

Take a Look at Flame Spread And Life Safety

ABOUT THE AUTHOR:

ONE OF THE PRINCIPAL factors blamed for loss of life in a fire is that of the flame-spread characteristic of the interior finish material. Note that the reference is to flame spread, not to flammability, combustibility or smoke contribution—just flame spread. This leads to the question what is flame spread? Flame spread is the term used to describe the rate at which fire or flame will propagate or move across the face of a material. The flames are supposedly developed or fed by the finish materials across which the flame moves.

Interior finish materials

A year or two ago a fire was specifically investigated because it was alleged that the manner in which the flames spread through the upper floor of the building was a perfect example of the results which can be expected through the use of interior finish materials with hazardous flame-spreading ratings. The fire originated in the reception room of a doctor’s office. From there it spread into the corridor. It so completely involved the corridor that the fire then spread into another doctor’s office at the far end of the building. Four persons were trapped on this upper floor and had to be rescued by the fire department through exterior windows. All preliminary and secondary reports indicated that the interior finish of the reception rooms and central corridor was responsible for the severity of the fire in which the four persons were trapped and two nearly died. Suspicion was directed mainly to acoustical tile.

Careful reconstruction of the event disclosed that at the time of the fire, the 14th coat of lacquer was being applied in one of the reception rooms. A spark from the paint spray compressor ignited the flammable vapors in the room. The one-half gallon or so of lacquer in the spray rig escaped as the machine was destroyed. A five-gallon can of lacquer and another five-gallon can of lacquer thinner were spilled to further contribute to the fire. The escaping vapors moved into the corridor and down the hallway and into the other reception room. The ceiling tiles in the first reception room and in the corridor immediately outside were badly charred. The evidence of charring of the ceiling tile lessened as the hallway lengthened. The upper portion of the corridor walls was badly damaged. Near the floor, the pattern in the vinyl wall covering could still be clearly seen. The floor tiles were unbumed.

Noncombustible acoustical tile

Investigation established that all the acoustical tile used was of the mineral type—in other words, noncombustible. The wall covering was of polyvinyl chloride in a thickness no greater than wallpaper, and with a flame spread rating of 1-10. The floor tiles were not involved in the fire. The combustible loading in the building was such that flammable gases were being released at such a rapid rate that they could not bum at the point of origin. These unburned gases traveled through the building and burned as they reached sufficient oxygen. But the combustible gases did not emanate from the interior finish which was of a type acceptable to both building and fire authorities. The interior finish was being singled out as the culprit when the real problem was with the building contents.

In the 1959 tests at the Robert Louis Stevenson school building in Los Angeles, considerable quantities of wood were burned—usually 1,400 pounds at a time. It was estimated that the average heat release per minute amounted to 374,000 Btu. The test fires generally originated on a landing just above the basement level. After approximately 10 minutes, when the temperature 8 inches below the ceiling at the center of the first-floor corridor and directly in line with the opening to the stairway to the basement reached 700 to 800° F, the ceiling tiles ignited and flame did propagate rapidly from the corridor. Records kept on the test indicated, however, that the corridor was untenable due to smoke within 2 minutes after the fire was ignited and untenable temperature conditions were reached within 2 minutes 45 seconds—7 to 8 minutes before the acoustical tile was ignited. In this case the interior finish material did serve as a wick or fire trail along which the fire could travel through the corridor. It did not in itself constitute a direct life hazard.

Additional tests

In 1960 additional tests were run at St. Agnes High School and fires were set in the corridors. The flames from wood cribs impinged directly against the acoustical tile ceilings. When a wood crib of 75 pounds was used the flame never propagated any great distance away from the area of impingement regardless of the flamespread rating of the tile. The tiles used had flame-spread ratings of from 3 to 92 with various ones at points between these extremes. When three cribs totalling 225 pounds in weight were used there was some flame spread down the corridor but it was of no great consequence. The estimated maximum average heat release was 135,000 Btu per minute. The peak intensity of the fires was developed in 2 to 3 minutes.

In the Santa Fe school tests in 1961, wood cribs of 340 pounds were employed. The estimated maximum average heat release was 180,000 Btu per minute. The corridor used in this school was but 8 feet in width while in the 1959-1960 tests the corridors were 12 feet wide. It was found that by using larger cribs, with more wood, the ceiling materials could be overpowered. For example, with 340 pounds of wood, and a red oak ceiling, the flame spread about 35 feet down the hallway. With 500 pounds of wood, the flame could be forced to run off the end of the red oak-covered ceiling 50 feet down the corridor. But, on investigation, it was found that the red oak at the end of the test area was not burned in itself but was only slightly discolored as a result of flames running across its surface. The flames which were causing discoloration had originated many feet back closer to the fire crib.

Continued on page 1068

FLAME SPREAD

Continued from page 1038

In other words, interior finish materials with a flame-spread rating of less than 100, as determined by Tunnel Test, ASTM E-84, do not appear to be self-propagating. Unless such materials are reinforced by the burning of the combustible load in the building or are heated slowly to temperatures of above 700° F so that they will “give off” combustible gases themselves, the materials present no undue hazard if flame spread alone is being considered. The real problem where life safety is concerned is with smoke.

A material with a low flame-spread rating and a high smoke-contribution factor can be hazardous. Such materials need regulation and specific limitations on its usage are necessary. A material with a high flame-spread rating—above 225—and a low smokecontribution factor needs regulation in. a similar manner. Materials with both high flame-spread and high smoke-contribution factors must be regulated prohibitively and with rather extreme limitations placed on its usage both as to the quantity or area in which it can be used and the types of occupancies in which it can be used.

When dealing with high life-hazard occupancies, particularly where the inhabitants are nonambulatory, semi-ambulatory, or confined, only materials with low flame spread and low smoke contribution should be used. When dealing with other life occupancies such as places of assemblage, theaters, apartment houses, hotels, schools, etc., some limitations need to be imposed. In exit ways which are truly exits, and so with little or no combustible loading, the currently recognized use of materials with a flame-spread rating of 75 is acceptable.

It is felt in some quarters that too much attention has been paid to the flame spread of building materials and not enough to other factors. A ceiling or wall covering that meets all requirements for flame spread is often covered with a coat of paint or varnish that completely nullifies its value. By the same token, a room that is enclosed with materials that are relatively flameproof frequently has contents that readily propagate flame, heat and smoke. These include overstuffed chairs, lacquered furniture, combustible room dividers and fixtures which normally become involved in a fire and contribute heavily to the smoke generated and the unburned gases of combustion which really spread the flames. Fire prevention efforts directed to contents and finishes, augmenting regulations governing building materials, may provide the answer to flame spread and life safety.

No posts to display