US3844354A - Halogenated fire extinguishing agent for total flooding system - Google Patents

Abstract

Chloropentafluoroethane is an efficient and economic fire extinguishing agent for total flooding systems.

Description

l 6 9 4 6 I 10-29-74 OR 398449354 Unlted States Patent 11 1 1111 3,844,354

Larsen Oct. 29, 1974 732: [54] HALOGENATED FIRE EXTINGUISHING 3,056,741 10/1962 Nugey 252/8 X AGENT O TQTAL FLOODING SYSTEM 3,276,999 10/1966 Petit et a1. 252/8 3,473,612 10/1969 P611165 t 169/11 1 Inventor: Eric Larsen, Mldland, Mlch- 3,529,670 9/1970 Herblil'le 169/Mk44" 4; F1;

[73] Assignee: The Dow Chemical Company,

Midland, Mich. Primary Examiner-M. Henson Wood, Jr. [22] Flled: July 1973 Assistant ExaminerMichael Y. Mar 21 APPL 37 102 Attorney, Agent, or FirmSidney J. Walker [52] US. Cl. 169/46, 169/11 [51] Int. Cl. A62c 5/16 58 Field 61 Search 169/1 A, 2 R, 5, 11,46; [57] ABSTRACT Chloropentafluoroethane is an efficient and economic [56] Ref r nce Cit d fire extinguishing agent for total flooding systems.

UNITED STATES PATENTS 7 2,641,579 6/1953 Benning 252/8 2 Claims, N0 Drawings HALOGENATED FIRE EXTINGUISHING AGENT FOR TOTAL FLOODING SYSTEM BACKGROUND OF THE INVENTION Total flooding systems (TFS) to extinguish fires is used where there is a fixed enclosure about the hazard that is adequate to enable the required concentration to be built up and maintained for the required period of time to ensure the effective extinguishment of the fire in the specific combustible materials involved where the ambient temperature is above -70F. Thus, these systems provide fire protection within rooms, vaults, enclosed machines, ovens, containers, storage tanks and bins.

Where possible, halogenated extinguishing agents are preferred in TFS because such agents do not cause water damage.

There are presently in use only two such halogenated extinguishing agents used for TFS. These are bromotrifluoromethane (Halon 1301) and bromochlorodi- LII fluoromethane (Halon 1,211). Of these two, Halon 1,301 is the only one that may be used .in normally occupied areas and then only in concentrations less than percent. A normally occupied area is defined as an area which is intended for occupancy.

From a performance viewpoint, a total flooding system is designed to develop a concentration of agent that will extinguish fires and combustible materials located in an enclosed space. It must also maintain an effective concentration until the maximum temperature has been reduced below the reignition point.

Although the above Halons are effective, they are relatively expensive because of their bromine content.

The bromine is present because it is regarded as having greater fire extinguishing effectiveness than chlorine.

For example, the concept of atomic resistivity" for the halogen atoms was put forth by J. E. Malcolm, Engineering Res. & Dev. Labs Rept. PB 106,268, Interim Rept. 1171, Aug. 18, 1950, vaporizing Fire Extinguishing Agents." Malcolm stated that it had been known previously that bromine was more effective than Flammability Peak 100/2 atomic resistivities For example, Halon 121 1 has one bromine, one chlorine and two fluorine atoms in the molecule and would i have a calculated flammability peak of F.P. 100/10 2 1+ 1=100/14= 7.1 volume No credit is given in this method for the hydrogen atoms in the molecule. Using Malcolm's equation, Halon 1301 has an F.P. of 7.7 volume percent.

Using Malcolm's equation, the compound of the present invention would appear to be unsuitable asits flammability peak equals 14.3 volume percent.

Other mechanisms have been postulated as to why halogens inhibit combustion. In all of these, it has been stated that bromine is generally 1% to 2 times as effective as chlorine.

SUMMARY OF THE INVENTION Based on studies I have made, 1 have concluded that the mechanisms heretofore promulgated as explanations of why extinguisher systems work have been overly concerned with the chemical structure and reactivity of the agents rather than taking full advantage of the physical characteristics of the various chemical agents available. I have concluded that both the inert gases and the halohydrocarbons act as a flame suppressant by increasing the total mass of gas in the system-to a point where the heat generated by one layer of burning gas is insufficient to heat an adjacent layer above the limit temperature of the gas, i.e., they behave strictly as heat sinks. l have found that nearly all halohydrocarbons containing less than weight percent halogen have flammable limits in air and that it is the weight percent halogen present in the molecule that is important rather than the type of halogen.

Proceeding on this premise rather than those previously advanced, i.e., a chemical mechanism of flame suppression, I applied my findings through the testing of chloropentafluoroethane as an extinguishant for a TFS. Based upon the previously advanced inhibiting mechanisms, one which is based on free radical process and the other based on the anionic activation of oxygen during combustion, this composition would only be V: as effective a fire suppressant as our Halon 1301 and 121 1. As will be shown below, this was not the case.

Total flooding systems as a means of fire control are a relatively recent development. Detailed information on these types of systems, their mechanical design as well as agent requirements are given in NFPA Bulletins No. 12A and 12B.

A fire extinguishing agent must be highly effective, nontoxic, thermally stable and electrically nonconductive for use in TFS since these systems are designed for use in enclosed areas which may be occupied during the use of the system.

Toxicity is of prime importance in that the occupants of an area protected by a TFS may be exposed to agent concentrations ashigh as 15 volume percent and their faculties must not be impaired by either the toxic or anesthetic properites of the agent. The importance of toxicity is shown by the fact that while Halon 1301 (CF Br) UL Toxicity Class 6 may be employed in concentrations of up to 10 volume percent in normally occupied areas, Halon 1211 (CF BrCl) UL Toxicity Class 5a may not be employed in normally occupied areas. This distinction is based entirely on the toxic properties of the agents since both have about the same fire extinguishing ability in TFS. In this regard, Halon 251 (CF CF Cl) has a UL Class of 6.

Apart from the acute toxicity of agents expressed by the UL classification, the narcotic, CNS, or anesthetic effect of the agent must be considered in TFS in areas that may be occupied. For example, Halon 1211 which shows an approximate lethal concentration for a 15- minute exposure of 32.4 volume percent cannot be employed in TFS for occupied areas at levels above about 4 volume percent unless egress can be carried out within one minute. This restriction is carried by Halon 121 1 because of time-dependent CNS activity at levels below 4 volume percent.

An additional requirement that is imposed on an agent which is to be used in TFS is that it boil at a temperature low enough so that its partial pressure under ambient conditions will produce an agent concentration in the vapor phase sufficient to extinguish the fire. Thisputs a practical upper limit on the boiling point of the agent at about 60C. For example, the compound C F C F boils at 100C. and hasv a saturated vapor pressure at 70F. of about 40 mm. (about 5 volume percent) which is less than the concentration required to inhibit flame propagation (6.8 volume percent).

With all these parameters in mind, 1 have found that chloropentafluoroethane (Halon 251) is a surprisingly effective fire extinguishant under TFS conditions. This compound is as effective as the agents CF Br and CF ClBr under TFS conditions. It falls into the UL Class 6 and does not show anesthetic effects or CNS activity. Moreover, it is considerably more economic to prepare because of the absence of bromine. Moreover, its physiological activity is less.

SPEClFlC EMBODlMENTS EXAMPLE 1 was evacuated and air allowed back into the system (1 mm.) A small amount of glass wool attached to a cop- 1 per wire was dipped into Nujol, a refined mineral oil, and lit with a match. The fire was allowed a 15-second preburn and then introduced to the flask, and the time to extinction of the flame measured. Average extinction time was 13.2 i 1 second. The above experiment was rerunrthree more times using the three Halons,

251, 1211 and 1301. The volumepercent of agent in each case was calculated from the partial pressure of agent added. Air was rapidly readmitted to the flask to bring the total pressure back to atmospheric and to mix the gases. The flask was open in each case and the flaming Nujol soaked wick inserted into the flask and the time to extinction of the flame measured. Volume percents of the various agents employed which gave a 2 second extinction time are shown in Table 1, below.

EXAMPLE 2 The above experiments were carried out using an ethylene flame in place of the Nujol soaked wick.

, When no agent was present, the extinction time of the flame was 24 seconds. The volume percents of the various agents required to give a 2-second extinction time are shown in Table 1, below.

' EXAMPLE 3 4 TABLEI V ol u rne Percent Required To Give A Two-Seem EfiiFetion Time Ethylene Basically the TFS requires release of the agent in an enclosed area when the presence of a fire is discovered. The amount of agent required depends upon the type -of fuel feeding the fire. The concentration shown in Table 1 show the minimum percentages required with several different fuels. Levels of 7-10 volume percent are preferred for general application. The use of excess amounts of agent, i.e., 15 percent, is wasteful of expensive agent, and can lead to excessive dilution of the oxygen level of the air. The use of too little agent fails to extinguish the flames, though it can slow the rate of flame propagation. It also can result in excessive smoke formation and probably in release of HF or HCL through decomposition of the agent.

It is to be understood that the compound of this invention can be used in mixture with other recognized fire extinguishants such as Halon 1301 and Halon 121 1. For example, a mixture of C F Cl and CF ClBr could be used in TFS whereas CF ClBr has limited utility because of toxicity in these systems. Such mixture could allow development of mixtures having maximum effectiveness at minimum cost and toxicity.

It is especially useful in TFS extinguishing systems in occupied areas where an electrically nonconductive medium is essential or desirable, where clean-up of other media presents a problem, or where weight versus extinguishing ability is a factor. Some of the hazards and equipment that chloropentafluroethane will protect are gaseous and liquid flammables, electrical hazards, engines utilizing flammable fuels, ordinary combustibles such as paper, wood and textiles, hazardous solids and electronic computers, data processing equipment and control rooms.

1 claim:

1. The process of extinguishing a fire in 'a normally occupied enclosure comprising introducing a volume of C F C1 sufficient to provide an extinguishing concentration and maintaining said concentration at a value of less than 15 percent until said fire is fully extinguished.

2. Theprocess of claim 1 wherein the volume percent of C F Cl is from about 7 to 10.

Claims (2)

1. THE PROCESS OF EXTINGUISHING A FIRE IN A NORMALLY OCCUPIED ENCLOSURE COMPRISING INTRODUCING A VOLUME OF C2F5CL SUFFICIENT TO PROVIDE AN EXTINGUISHING CONCENTRATION AND MAINTAINING SAID CONCENTRATION AT A VALUE OF LESS THAN 15 PERCENT UNTIL SAID FIRE IS FULLY EXTINGUISHED.

2. The process of claim 1 wherein the volume percent of C2F5Cl is from about 7 to 10.