3. In apparatus for preventing and extinguishing oil well fires around a well casing, a source of refrigerated, pressurized carbon dioxide; at least one nozzle positioned adjacent the exterior of the well casing; a conduit extending between the source of carbon dioxide and the nozzle; a valve in the conduit for controlling the flow of carbon dioxide therethrough; and means coupling the conduit with the exhaust pipes of engines adjacent to the well casing for dispensing carbon dioxide thereon when the valve is opened.

4. In apparatus for preventing and extinguishing oil well fires around a well casing, a source of refrigerated, pressurized carbon dioxide; at least one nozzle positioned adjacent the exterior of the well casing; a conduit extending between the source of carbon dioxide and the nozzle; a valve in the conduit for controlling the flow of carbon dioxide therethrough; a motor connected in driving relation with the valve; an energizing circuit connected to the motor; a source of electricity in the energizing circuit; current-responsive switching means in the energizing circuit; a closed sensing circuit connected to the electrically responsive switching means adapted to cause the switching means to hold the energizing circuit open as long as current is flowing in the sensing circuit; a source of electricity in the sensing circuit; and at least one switch in the sensing circuit whereby opening the switch in the sensing circuit causes the current-responsive switching means to close the energizing circuit to open the valve.

8. In apparatus for extinguishing combustion of fluids blown out of a well casing head, dispensing means adjacent said head; a conduit connected to the dispensing means; a valve in the conduit; means communicating with the conduit for forcing carbon dioxide through the conduit when the valve is opened; and actuating means arranged to open the valve by any of the following: change of temperature to a predetermined level at the wellhead; or change of air pressure to a Predetermined level at the wellhead.

9. In apparatus for preventing and extinguishing oil well fires around a well casing on an offshore drilling platform, a source of refrigerated, pressurized carbon dioxide; at least one nozzle positioned adjacent the exterior of the wall casing; a conduit extending between the source of carbon dioxide and the nozzle; a valve in the conduit for controlling the flow of carbon dioxide therethrough; and means for securing the source of carbon dioxide to the leg of the offshore drilling platform below water surface.

10. In apparatus for preventing and extinguishing oil well fires around a well casing head, a container; carbon dioxide in the container; means communicating with the inside of the container to maintain the carbon dioxide under pressure; means communicating with the inside of the container to maintain the carbon dioxide under refrigeration; dispensing means for carbon dioxide adjacent the exterior of the casing head; a conduit extending between the container and the dispensing means; a valve for controlling the flow of carbon dioxide through the conduit; current-reponsive actuating means constructed and arranged to open the valve when current is supplied thereto; an energizing circuit connected to the current-responsive actuating means; a source of electrical current in the energizing circuit; a current-responsive relay having contacts in the energizing circuit between the source of current and the actuating means; a coil in the relay; a core in the relay arranged to maintain the contacts open when current is supplied to the coil; a sensing circuit connected to opposite sides of the coil; a second source of electrical current in the sensing circuit; and heat-responsive switching means in the sensing circuit positioned near the casing head for opening the sensing circuit thereby closing the energizing circuit to open the valve when the temperature at the casing head reaches a predetermined value.

11. In apparatus for preventing and extinguishing oil well fires around a well casing, a source of extinguishing fluid; at least one nozzle positioned adjacent the exterior of the well casing; a conduit extending between the source of extinguishing fluid and the nozzle; a first valve in the conduit for controlling the flow of extinguishing fluid therethrough; a motor connected in driving relation with the first valve; an energizing circuit connected to the motor; a source of electricity in the energizing circuit; current-responsive switching means in the energizing circuit; a closed sensing circuit connected to the electrically responsive switching means adapted to cause the switching means to hold the energizing circuit open as long as current is flowing in the sensing circuit; a source of electricity in the sensing circuit; at least one switch in the sensing circuit positioned such that opening the switch in the sensing circuit causes the current-responsive switching means to close the energizing circuit to open the valve; and pressure-responsive means for opening the switch in the sensing circuit at a predetermined pressure.

12. In apparatus for preventing and extinguishing oil well fires around a well casing, a source of extinguishing fluid; at least one nozzle positioned adjacent the exterior of the well casing; a conduit extending between the source of extinguishing fluid and the nozzle; a first valve in the conduit for controlling the flow of extinguishing fluid therethrough; a motor connected in driving relation with the first valve; an energizing circuit connected to the motor; a source of electricity in the energizing circuit; current-responsive switching means in the energizing circuit; a closed sensing circuit connected to the electrically responsive switching means adapted to cause the switching means to hold the energizing circuit open as long as current is flowing in the sensing circuit; a plurality of switches connected in series in the sensing circuit; heat-responsive means for opening at least one of the switchEs at a predetermined temperature level; and pressure-responsive means for opening at least one of the switches at a predetermined pressure level.

13. In apparatus for extinguishing combustible fluids adjacent a wellhead, pressure-sensing means adjacent the exterior of the wellhead adapted to generate a signal when air pressure reaches a predetermined level; and dispensing means in communication with the inside of the well adapted to dispense noncombustible fluid into the well responsive to a signal generated by the sensing means.

14. In apparatus for extinguishing combustion of fluid issuing from a well, a manifold around the exterior of the casing, said manifold having at least one opening therein to direct carbon dioxide toward the stream of fluid flowing from the well; dispensing means communicating with the inside of the well casing positioned to form a venturi to mix carbon with the fluid in the casing; and means to release liquified carbon dioxide through the opening in the manifold and through the dispensing means such that carbon dioxide will be drawn into and encompass a fire and will mix with fluid before issuing from the well.

15. In apparatus for preventing and extinguishing oil well fires around a well casing, a source of refrigerated, pressurized carbon dioxide; at least one nozzle positioned adjacent the exterior of the well casing; a conduit extending between the source of carbon dioxide and the nozzle, a first valve in the conduit for controlling the flow of carbon dioxide therethrough; a branch line extending between the conduit and the inside of the well casing; a check valve in the branch line; the directional flow through the branch line being toward the well casing; a bypass conduit communicating with said conduit and connected thereto on opposite sides of the first valve; a second valve in the bypass conduit for regulating the flow of carbon dioxide therethrough; electrically operated means for opening the first valve; an energizing circuit connected to the electrically operated means; a source of electricity in the energizing circuit; switching means in the energizing circuit adapted to energize the electrically operated means to open the first valve causing carbon dioxide to be dispensed through the nozzle; and heat-responsive means positioned adjacent the exterior of the well casing for manipulating the switching means when the temperature adjacent the exterior of the casing reaches a predetermined value.