Fire Extinguishing Methods Utilizing 1-Bromo-1,1,2,2-Tetra-Fluoroethane

1. Field of the Invention

This invention relates extinguishing methods utilizing 1-Bromo-1,1,2,2-tetra-fluoroethane, HCF.sub.2 CF.sub.2 Br.

2. Description of the Prior Art

The use of certain bromine, chlorine and iodine-containing halogenated chemical agents for the extinguishment of fires is common. These agents are in general thought to be effective due to their interference with the normal chain reactions responsible for flame propagation. It is taught in the art that the effectiveness of the halogens is in the order I>Br>Cl>F, for example, C. L. Ford, in Halooenated Fire Suooressants, R. G. Gann, ed., ACS Symposium Series 16.

The use of iodine-containing compounds as fire extinguishing agents has been avoided primarily due to the expense of their manufacture or due to toxicity considerations. The three fire extinguishing agents presently in common use are all bromine-containing compounds, bromotrifluoromethane (CF.sub.3 Br), bromochlorodifluoromethane (CF.sub.2 BrBI), and dibromotetrafluoroethane (BrCF.sub.2 CF.sub.2 Br). Although a number of compounds have been considered as potential extinguishing agents, 1-bromo-1,1,2,2-tetrafluoro-ethane is not among them.

Although the above named bromine or chlorine-containing agents are effective in extinguishing fires, totally halogenated agents such as CF.sub.3 Br and CF.sub.2 BrCl, containing bromine or chlorine are asserted by some to be capable of the destruction of the earth's protective ozone layer.

It is therefore an object of this invention to provide a method for extinguishing fires that extinguishes fires as rapidly and effectively as the presently employed agents, and is environmentally safe with respect to ozone depletion.

The foregoing and other objects, advantages and features of the present invention may be achieved by employing 1-bromo-1,1,2,2-tetrafluoroethane (HCF.sub.2 CF.sub.2 Br) and blends thereof with other compounds as fire extinguishants for use in fire extinguishing methods and apparatus. More particularly, the method of this invention involves introducing to a fire 1-bromo-1,1,2,2-tetrafluoroethane in a fire extinguishing concentration and maintaining such concentration until the fire is extinguished. 1-Bromo-1,1,2,2 -tetrafluoroethane may be used alone or in admixture with other compounds, optionally in the presence of a propellant. Generally 1-bromo-1,1,2,2-tetra-fluoroethane or its mixtures with other compounds are employed in the range of about 1 to 15%, preferably 3 to 10%, on a v/v basis.

In accordancde with the present invention, 1-bromo-1,1,2,2-tetrafluoroethane has been found to be an effective fire extinguishing agent at concentrations safe for use. However, because 1-bromo-1,1,2,2-tetrafluoroethane contains a hydrogen atom, it has a very low ozone depletion potential due to its removal in the troposphere via reaction with hydroxyl radicals. For example, employing the method of Babson for the estimation of ozone depletion (ODP) values, 1-bromo-1,1,2,2-tetrafluoroethane has an ODP of 1.00, compared to ODP values of 14.26 and 2.65 for the presently employed agents CF.sub.3 Br and CF.sub.2 BrCl, respectively, a reduction in ODP of greater than 62% in each case.

1-Bromo-1,1,2,2-tetrafluoroethane has an LC50 value (concentration necessary to cause death in half of test subjects) of 19% v/v as reported in Int. J. Quantum Chem., Q Biol Symp 3, 171 (1976), and hence is effective at concentrations well below levels harmful to living things.

1-Bromo-1,1,2,2-tetrafluoroethane may be used alone or in admixture with other compounds, optionally in the presence of a propellant. Among the compounds with which 1-bromo-1,1,2,2-tetrafluoroethane may be blended are chlorine and/or bromine containing compounds such as CF.sub.3 Br, CF.sub.2 BrCl, CF.sub.3 CF.sub.2 Cl, and BrCF.sub.2 CF.sub.2 Br. Other compounds forming useful blends with, 1-bromo-1,1,2,2-tetrafluoro-ethane include CF.sub.2 HBr,CF.sub.3 CHFBr, CF.sub.3 CF.sub.2 H, CF.sub.3 CHFCF.sub.3, CF.sub.3 CHFCl, CF.sub.3 CHCl2, CF.sub.4, CF.sub.3 H and similar fluorocarbons. 1-Bromo 1,1,2,2,-tetrafluoroethane may also be used in the presence of a propellant, such as N.sub.2, CO.sub.2 or Ar.

Where 1-bromo-1,1,2,2-tetrafluoroethane is employed in blends, it is desirably at a level of at least about 5 percent by weight of the blend. 1-Bromo-1,1,2,2-tetra-fluoroethane is preferably employed at high enough levels in such blends so as to minimize the adverse environmental effects of chlorine and bromine containing compounds.

1-Bromo-1,1,2,2-tetrafluoroethane may be effectively employed at substantially any minimum concentration at which the fire may be extinguished, the exact minimum level being dependent on the particular combustible material, and the combustion conditions. In general, best results are achieved where 1-bromo-1,1,2,2-tetrafluoroethane or mixtures and blends are employed at a level of about 4% (v/v). Likewise the maximum amount to be employed will be governed by matters of economics and potential toxicity to living things. About 15% provides a convenient maximum for use of 1-bromo-1,1,2,2-tetrafluoroethane and its mixtures thereof in occupied areas. Concentrations above 15% may be employed in non-occupied areas, with the exact level determined by the particular combustible material and the conditions of combustion.

1-Bromo-1,1,2,2-tetrafluoroethane may be applied using conventional application techniques and methods used for agents such as CF.sub.3 Br and CF.sub.2 BrCl. Thus, the agents may be used in total flooding systems, portable systems or specialized systems. Thus, as is known to those skilled in the art, 1-bromo-1,1,2,2-tetrafluoroethane may be pressurized with nitrogen or other inert gas at up to about 600 psig at ambient conditions.

Practice of the present invention is illustrated by the following examples, which are presented for purposes of illustration but not of limitation.

Concentrations of agent required to extinguish diffusion flames of n-heptane were determined using the cup burner method. Agent vapor was mixed with air and introduced to the flame, with the agent concentration being slowly increased until the flow was just sufficient to cause extinction of the flame. The data are reported in Table 1, which demonstrate the effectiveness of HCF.sub.2 CF.sub.2 Br. Values for CF.sub.3 Br and CF.sub.2 BrCl are included for reference purposes.

The procedure of example 1 was repeated employing n-butane as fuel. Results are shown in Table 2, and demonstrate the efficacy of HCF.sub.2 CF.sub.2 Br for extinguishment of fires.

It can be seen from eh tables that HCF.sub.2 CF.sub.2 Br is as effective as the presently employed fire extinguishing agents CF.sub.3 Br and CF.sub.2 BrCl. The use of HCF.sub.2 CF.sub.2 Br in accordance with this invention is highly effective and its use avoids the significant environmental handicaps encountered with totally halogenated agents.