similar profile to the other curves reaches 90 u00b0 f in about 137 hours 5 7 days it can be seen therefore that as the difference between the dispensing to temperature of the chilled nitrogen foam and 90 u00b0 f increases there is a substantial calculated decrease in the time required for the surface temperature of the coal to reach 90 u00b0 f the safe temperature at which personnel can reenter the mine when the chilled nitrogen foam is dispensed at a temperature of 55 u00b0 f the calculated reduction in time is slightly greater than 50 as compared to nitrogen foam injected at ambient 72 u00b0 f temperature when injected at 60 u00b0 f the calculated reduction in time as compared to ambient nitrogen foam is around 46 this represents a quicker return to operations and a substantial savings to the mine operators as well as an early return to work and full pay for the mine workers when the foam is dispensed at a reduced temperature from the foregoing thermal analysis it appears that the lower the temperature of the nitrogen the more effective is the nitrogen chilled foam in reducing the time to bring the surface temperature of the involved area to 90 u00b0 f accordingly depending upon the size and efficiency of the chiller it is within the scope of the invention to chill.