Sprinkler Tests Answer Heat Rating Questions
The St. Louis, Mo., Fire Marshal’s Office has been under pressure from various sources to approve sprinkler head ratings higher than 165°F. Justification for these high-temperature heads is “reduced water demand.”
The unanswered questions were:
- How can reduced water demand be important where rooms or corridors have only one or two heads?
- To effectively reduce water demand, the sprinkler heads at the perimeter of the fire zone must be delayed to the point of not opening. Hence, how much delay results from higher temperature heads?
- If heads of lower temperature are used, could accelerated operation be expected? And if so, how much?
The above questions were triggered by the St. Louis fire marshal’s involvement with several completely sprinklered motels and residential occupancies. Determination to recommend the best life safety sprinkler systems in these buildings ultimately led to a challenge of the simplistic fad: “Use higher temperature heads and reduce water demand.”
Need for tests
The Fire Protection Technology Department at St. Louis Community College at Forest Park assisted the Fire Marshal’s Office in answering the above questions. Published literature was of little help because it was generally oriented toward industrial risks and therefore pertinent to large systems and high temperatures.
It was soon evident that answering these questions would require a unique test program, and since neither the college nor the Fire Marshal’s Office had a test program budget, ingenuity became the top priority.
The St. Louis Fire Department Training School had a smoke room equipped with automatic sprinkler piping. Also available were an old steel bed frame, a stack of old mattresses, some old sheets, a large supply of scrap wood and some dedicated fire department officers—Captain Charles Benning, Captain George Jenkerson, Captain John O’Shaughnessy, Fire Inspector Cliff Gross, and Fire Inspector Walter Miller. Chief Charles Kamprad and Fire Marshal Thomas Long gave their permission to use the personnel and equipment.
Faculty members assist
The Community College at Forest Park had an Instralab solid state digital reader, some type K (Chromel-Alumel) sensors, and two faculty members who are professional fire protection engineers, E. C. Hrbacek and myself. Both Hrbacek and I have served as volunteer consultants to the Fire Marshal’s Office for many years.
The Fire Department Superintendent of Equipment Jack Manning and an electrician wired the thermocouple sensors in place.
The St. Louis Automatic Sprinkler Corporation contributed 1978 sprinkler heads of various temperature ratings.
The equipment setup was checked out, and one burn was carried through to completion. Some minor setup revisions were made, and on January 11, 1978, all six tests were run.
Engine 2 assisted with the tests by manning a booster line, placing mattresses, removing the burned wastes, and cleaning up.
In the test procedure, a single bed was placed in a simulated motel room, 12 feet 7 inches by 16 feet 4 inches.
Sensors 1 and 3 were type K (Chromel-Alumel) thermocouples, reading through a multichannel digital reader. Sensor 2 was a Taylor mercury thermometer 100-900°F, with 10-degree graduations. The timer was a stopwatch.
The fuel was 5 pounds of scrap 1 x 2 lumber in 4 to 8-inch lengt hs, 1 pound of unglazed newsprint, a cotton-filled mattress and a cotton sheet.
The 5 pounds of wood and approximately half a pound of newsprint were placed in a 12 x 12 x 10-inch-deep metal box with sides and bottom perforated with 1-inch-diameter holes. The box was set on a wire stand and was 3 inches above the floor. The bed sheet was spread properly over the mattress, and half a pound of newsprint was scattered on the bed. (An average copy of a city daily newspaper approximates 1 pound of newsprint.)
The newspaper in the fire box was lit with a match. The stopwatch was started when burning of the paper was evident. The “torch man” then left the room and the door was closed. Burning proceeded until the sprinkler head was activated, when the watch was stopped and Engine 2 cleaned up and prepared for the next burn.
Temperatures from each sensor were read and recorded just prior to ignition. Then readings were recorded at 60-second intervals until completion of each burn. The watch was stopped when the head was activated and the time of activation was recorded.
Graph data explained
The time-temperature curves in the graph are compilations of data taken from the fire burns. The dip in the curve for temperatures 6 feet above the floor corresponds to the burning out of the newsprint on the surface of the bed prior to active burning of the sheet and mattress.
Readings 2 feet 4 inches below the ceiling were lower than might be expected because sensor 1 tended to be on the perimeter of the thermal column and below the heat strata at the ceiling.
The most consistent temperature readings were 1 ½ feet above the floor.
Smoke obscuration readings were not taken, but ability to see objects across the room (16 feet) at 5 feet above the floor ceased at approximately 2 minutes after ignition.
The average time to activate the 135° heads was approximately 2.5 minutes less than the time required to activate the 165° heads.
The 212° head had not activated at 20 minutes, and the test was terminated.
It took only about 10 seconds for the other sprinkler heads to extinguish each fire.
The amount of energy required by the sprinkler heads for activation is approximately in the ratio of the AT between starting room temperature and activation temperature.
Also, energy available for absorption by the sprinkler head is relative to the area between the time-temperature curve of the air near the ceiling and the time-temperature curve of the sprinkler head. Fig. 1 indicates an average activation time of approximately 8.5 minutes for 165° heads, and 6.0 minutes for 135° heads. Also there was a AT of approximately 100° F for the 165° heads, and 70°F for the 135° heads, from starting temperature.
It is apparent that the areas between the ceiling time-temperature curve and the sprinkler head time-temperature curve are in the approximate ratio of 100 to 70 (AT = 165°F – 65°F, and AT = 135°F – 65°F).
If an automatic sprinkler head had been available with a 105° rating, the AT above starting room temperature would have been 40° F, and the requisite area between the time temperature curves would be approximately 40/100 of the area between the 165°F curves. The time interval to accomplish this would have been approximately 3.5 minutes.
- In a residential occupancy, the use of high temperature sprinkler heads will delay activation and render the life safety capabilities of the system worthless.
- Sprinkler heads rated at 135°F will operate approximately 2.5 minutes sooner than 165° heads in the low-fueled fires typical of residential occupancy.
- If 105° heads were available, they would probably have operated approximately 5 minutes sooner than the 165° heads.
- Time of operation could have been shortened by approximately 0.5 minute for all heads with a starting room temperature of 80° F.
- During the burns, temperatures near the floor climbed very slowly, reinforcing the concepts taught by the NFPA Learn Not to Burn program.
Lower-rated heads feasible
Modern commercial residential facilities (nursing homes, apartments, motels, etc.) are air-conditioned and compartmented. Summer temperatures in bedrooms are not likely to exceed 90°F, or drop below 32°F in winter. In such controlled environments, a sprinkler head temperature below the conventional 135° head is justified. Reducing activation time by five minutes can spell the difference between success and disaster or life and death in a residential life safety situation.
Smoke detection is a necessity in all residential sleeping rooms. Low temperature heads cannot save the occupants in the rcxmi of origin of fire. 1’hey can only extinguish the fire and confine it.
Further testing should be done to:
- Test some experimental heads rated at 105° F.
- Compare the tests reported here with results in a room having walls with lower heat absorption (dry wall construction).
- Monitor CO and CO2 during the burns.
- Compare quartzoid with eutectic heads for speed of activation.