li the Chemical Laboratory I
Edited bv N O R M A N V. STEERE. 140 Melbourne Ave., S E . Minneopolir, Minn. 5541 4
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Another investigation a t about the same time indicated a related phenomenon. A contact cement contained flammable solvents; however the flash point of the entire solution was significantly lower than the flash point of any of the constituents. The resultant mixture was in the same flash point hazard range as gasoline. Both of these eases had one common denominator-the combustible or flammable liquid was contained in a media with a high surface to mass ratio, fabric in one case and the glue in the other. Therefore, mare surface of the liquid was exposed to the atmasphere than in a normal liquid layer of the same projected surface area. Theoretically this should not make a difference. The vapor pressure should be the same a t all surfaces and the concentration of the vapor is proportional to the vapor pressure. The first explanation considered for the rapid fire spread was that the cloth fabric ignited, preheated the combustible liquid and the fire spread was accelerated. In a burning test of cotton fabric, the same type of fire development occurred. These tests were made a t an ambient temoerature of
CXXXI. Flash Fires with High Flash Point Liquids* John A. Campbell, Manager, Chicago Office, Gage-Babcock & Associates, 135 Addison ~ l k h v r s t lllinois , 60 126 Some routine flash point and flammability tests we ran in conjunction with recent loss investigations yielded some uneapeeted results. First, flash fires were obtained a t ambient temperatures 70'F or 3 9 T below the flash paint of the liquid. Second, on some bonding agent mixtures we abtained flash points more than 30'F or 1 7 T below the flash point of any components in the mixture. The most common eireumstance under which this type of fire is likely t o occur will probably also produce serious or fatal iniuries. The results of this work have also indicated to us that: the current lOOD (37.8%) division point between flammable and combustible liouids is too low for all applications; users are not being provided with adequate warning on the hazards of combustible liquids, and some products should possibly be banned for domestic use. Flash point is defined as the lowest temperature of a liquid a t which it gives off vapor sufficient to form an ignitible mixture with air near the surface of the liquid or within the vessel used. By ignitible mixture is meant a fuel-air mixture within the flammable range that is capable of propagating flames away from the source of ignition. Flash points are determined by standard ASTM open cup and closed cup methods using a pilot flame ignition. The significance of flash point can be illustrated by placing a mateh in a tray containing a thin layer of liquid with a flash point higher than the ambient temperature. If you are not careful, the liquid will put the match out as effectively as water. However, if the mateh is inserted carefully so that the burning part is not submerged, i t will continue t o burn and vaporize some of the liquid. Burning will continue but will be localized about the match and fire will not propagate aver the surface. T o get fire to spread over the surface of a liquid cooler than its flash point temperature, it is necessary to: preheat the liquid to its flash point temperature, or mechanically spread the flame, or apply a massive ignition source which effectively preheats enough of the liquid so that the resultant fire is selfpropagating. However, if a mateh is inserted in a tray of liquid having a flash point below amhient temperatures, the fire rapidly spreads over the entire surface.
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We know that flash fires can occur if a liquid is finely atomized even though both ambient and liquid temperatures are well below the flash point. In addition, if a large enough fire is started in the spill of a liquid the fire itself can preheat the liquid and the fire can be self propagating. I t is also recognized that if a fire is started in other materials which are wet with the liquid, the combustible liquid can accelerate the combustion even though it is initially a t a temperature below its flash paint. However, i t is common to consider liquids with flash points above normal ambient temperatures to be "relatively" safe. The normal warnings provided for these liquids and assoeiated safety recommendations are considerably less than for liquids with law flash points. This work was prompted by the investigation of a fire in which serious injury had occurred. An individual had splashed a mineral spirits solvent on his elothing and about 20 min later sparks from a cutting torch dropped on the bottom of his trousers. Fire rapidly involved much of the elothing he was wearing. The description of the incident suggested that combustibility of the clothing could have been the most significant factor since the flash point of the solvent was 110°F (43.3Y2) and the ambient temperature ahout 67'F (19.4T). If the clothing had become well involved in fire, some residual solvent that had not evaporated could also accelerate the combustion. Tests were made on the fabric, a 7 oz. dacronleotton blend, and it burned hut with no more speed and intensity than normal elothing. Attempts to ignite the clothing with sparks from a cutting torch were made; ignition could only be obtained with great difficulty. Next, a sample of the fabric was wet with solvent, allowed to dry for 20 min and sparks were allowed to drop on the material. Ambient temperature and temperature of the liquid and fabric were 68°F (20PC). Ignition occurred promptly and fire rapidly spread over the entire sample.
the cotton showed no signs of combustion. To isolate the combustibility of the fabric as a factor, tests were conducted using the same mineral spirits solvent but with a 24 oz. woven asbestos fabric. The asbestos fabric contained no sizing or other material that would ignite when subjected to a pilot flame. The asbestos fabric was dampened with the mineral spirits and a pilot flame applied. It quickly became enveloped in flame. This demonstrated that the combustibility of the fabric was not necessary for the development of this type of fire. The same test was repeated with the woven asbestos fabric in the vertical position-the fire development and spread was very rapid. Comparison of the combustion of mineral spirits on the asbestos and an the dacronlcotton blend were also made. The asbestos being a much heavier fabric could absorb more of the mineral spirits; it burned more vigorously than the lighter fabric. A direct comparison of combustion of a dry fabric and a dampened fabric was made with a 5 oz. dacronlcotton blend using the same mineral spirits solvent. The ambient temperature was 70°F (21.1°C). (Continued on page A l l l J
Table 1 -
L i a u i d r used
Flash o a i n f f e m o e r a t u r e
pint t h i n n e r ~ i n e r a ls p i r i t s
Decane Charcoal lighter
'Presented a t the National Fire Proteetion Association annual meeting, Miami, May, 1974.
Kerosene ~ o m laundry e roil & stain remover soray Home laundry antistatic agent
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Table 2.
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Materials Tested
C o t t o n cloth. 3 oz. c o t t o n cloth. 3114 oz. Gauze-like cleaning web Dacron-cotton blend 65135%. 5 oz. Dacran-cotton blend 65135%. 7 % ol. Woven asbestos. 11 or. woven asbertos. 24 0 2 . ond ding cement Silica gel P O ~ O U I sintwea bronze sheet
Two fabric samples were suspended vertically, one was dsmpened with the solvent and the other remained dry. A pilot flame was applied t o the dry sample first and immediately thereafter to the dampened sample. The dampened sample became totally involved before any significant flame spread was observed on the dry sample. Even as the fire involving the dampened sample subsided there was only a partial spread on the dry sample. This identical test was repeated with the same fabric hut one sample was wet with gasoline and the other with the mineral spirits solvent. Both were allowed to dry for 20 min before a pilot flame was applied. The gasoline had effectively evaporated during that time interval and the sample that had been wet with gasoline burned similarly to the dry cloth. However, the less volatile mineral spirits remained and the sample that had been wet with this solvent burned vigorously. During the test program, we evaluated liquids with flash points from 105°F (40.6'C) for a paint thinner to 140°F (60°C) for kerosene, Tshle 1. All the listed flash points were determined by the open cup test method except for decane which was not tested. The published flashpoint of decane is noted in this table. Two household laundry products were also tested, one of which was not even labeled as combustible. The materials used included fabrics and other materials which would feature a high surface to mass ratio, Table 2. Ignition in most of the tests was a pilot flame just as is used in flash point testing although cutting torch sparks were used in the first series. Electric spark ignition was not used because we helieved the principal ignition
Table 3. Horizontal Flame Spread-3 105°F 140.6"Cl Flash Point Thinner Thinner "red
02.
hazard in this type of circumstsnce would be open flame or cuttinglwelding torch particles. Table 3 summarizes the results of testing conducted a t 50DF (lODC)ambient using cotton cloth samples dampened with 105OF (40.ti°C) flash point paint thinner. The flame spread after s 10 min delay was 4% times that aver a dry surface. Even after 25 min of drying time the flame spread was 3 times greater over the surface of the sample that had been dampened than the dry sample. Tests using a common household gauzelike cleaning web (cheesecloth) and same common home products are summarized in Table 4. Since the cleaning web itself was relatively combustible the flame spread multiplier was less than far the cotton cloth. One of these two household products tested which gave a definite increase in the flame spread, had no combustibility warning on the container. The horizontal flame spread of several different materials, both dry and after being dampened with mineral spirits (105°F or 40.6"C flash point) and with kerosene (140PFor 60°C flash point), 1s itemized in Table 5. Again the fire spread multiplier for a typical cotton fabric is about 4% far the mineral spirits For the higher flash point kerosene it is about 3%-The increase in fire spread was even more significant on the dacron-cotton blend than the cotton. Although the actual flame spread across the blend samples was less, the flame spread across the dry blend was very low and the multiplier was about 18. The higher flame spreads in this series were related to weight of the fabric rather than the combustibility of the fabric. However, the heavier weight fabrics could absorb more liquid and therefore once ignited, the resultant fire was larger and sustained longer. The vertical flame spread is much greater with both dry and moist fabrics as illustrated in Table 6. In the vertical position the spread is sufficient so that I would definitely call it a flash fire. In the tests, the heavier asbestos fabrics showed a higher flame spread than the lighter blended fahric. The effect of drying time on tests using mineral spirits and 11 oz. asbestos fabric is presented in Table 7. There is a general (Contmued on page A112J
Cotton Cloth-50°F llO°CI-Ambient
Drying r i m e irnin1
Weight of absorbed thinner @ ignition (9)
Flame spread iin.110 rec1
Table 4. Horizontal Flame SpreadSaure.Like Cleaning Web Ambient Temperature-5OsF llODCl
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CO"difi0" of sample
DIY D a r n ~ e n e dw i t h 1 0 5 ' ~1 4 0 . 6 ° ~flash ~ ~ o i n tninner t
Flame spread ( i n 1 1 0 recl 6 20
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trend for the flame spread to be reduced the longer the material dried. However, hazardous conditions still existed over 20 min after the material had been dampened. I t was also interesting that the resultant fire was more difficult to extinguish on fahrics which had dried the longer periods of times. When the data point was reached, a stream from a 2% gal pump tank was used t o quickly douse the flames. However, as the drying time for these asbestos fabrics increased the resultant fires became noticeably more difficult to extinguish. A number of tests were also made to cross-check the results and evaluate possible explanations for this mode of ignition and fire development. Decane, a pure hydrocarbon, was tested t o determine if the phenomena were unique to mixtures. Tests were also conducted with silica gel saturated with kerosene to compare the behavior with a nonfahric-type material. The initial work had shown a similar phenomena had occurred with a bonding agent. A porous sintered bronze sheet was wet with decane to determine if the small amount of liquid on its surface and the high cooling capacity of the bronze would prevent the development and spread of fire. Fire propagation over the surface of the liquid-dampened media occurred in all of these tests. The rapidly developing fires which occurred with the high flash point liquids is hazardous in the vertical mode of flame spread. This mode of spread would be the one commonly associated wlth incidents in which such materials were splashed on clothing. However, significantTable 5.
ly accelerated flame spread also occurred both horizontally and downward and with both combustible and noncombustible absorbing media. Warnings provided on containers of flammable liquids emphasize the fire hazard t o users. However, the user of a combustible liquid receives a relatively low key warning because its flash point is above normal ambient temperatures. Present standards define a flammable liquid as one with a flash point under 100°F (37.g°C), and a combustible liquid as one with a flash paint over this. However, as we have illustrated here, it is possible under commonly encountered conditions t o have flash fires with combustible liquids a t temperatures well under their flash points. The 100°F (37.8'C) division point is reasonable for transportation of flammable and combustible liquids: however, in the actual use of these liquids a higher division point would be recommended, better warnings should be provided for users and more stringent safety precautions established for handling these liquids. The two incidents which prompted this work are not necessarily isolated or rare happenings. The July 1973 Fire Journal describes a fatal fire in the Sears Tower which appears to have many similarities to the incidents described. The May 1974 Fire Journal also describes a fatal fire involving kerosene splashed on an individual's clothing. Many other fire reports were found which could have been caused by the phenomena. The reports often indicate an uncertainty as to what liquid was involved or assumed that the clothing was initially ignited. However, as we have shown here these incidents can occur even with noncombustible clothing.
Horizontal Flame Spread-70°F l21.1'Cl Ambient-l mi" Drying Time F l a m e soread
ii"./lO sec1
~ i n e r a rplritr l
i i i o ' ~or 43.3-c Materials
No liquid
~ l a r hPoint)
Kerosene ( 1 4 0 ' ~ or 6 0 ' ~Flash Polntl
Cotton. 3% o z . Dacron-cotton blend 65135%. 7% 02. woven asbertor. 1 1 oz. woven asbestos. 2 4 o z .
2.5 .5
11.3 9.1
8.6 5.4
6.2 4.6
3.9 2.3
Table 6.
0 0
Vertical Flame Soread 70'F 1Z1.loC1 Ambient 1 min Drvins Time Flame spread. (in.!lO recl
Materials Cotton. 33b 0 2 . Dacron-cotton blend 65135%. 71h Or. woven arbertor, 1 1 oz. Woven arbertor, 2 4 or.
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1lQ"ld
Mineral rpir,ts ( 1 1 0 " ~or 4 3 . 9 ~ Kerosene 1 1 4 0 ' ~ or 60°C flash point] F I ~ paint) S ~
34.8 11.5
141.4 87.5
105.3 66.6
0 0
135.5 113.5
76.4 70
Table 7. Effect of D w n g Ttme on Vertical Flame Spread Woven Arbertor. 24 02.: Mmeral rplr.tr Ambwnt Temperature-70 F 121.1 C I . . . . -. .- -. Drvina time ( m i n l
A 1 12 / Journal of ChemicalEducation
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Flame spread I i n i l O recl
