Study of characteristics of fire hazard

Laboratory work 9

Study of characteristics of fire hazard

 

Objective: learning the basic indicators of fire and explosion hazards of substances and materials, types of combustion, methods for assessing the explosion and fire objects and procedure of determining the flash point and ignition of the liquid fuel.

 

Determination of flash ignition temperature of the liquid fuel

 

Increasing the pressure increases the flashpoint. The interrelation between a flash point at normal pressure and t₇₆₀ and t_p at different flashpoint barometric pressure ρ (mm of mercury) is expressed by the empirical formula

          t ₇₆₀ = t _р + 0,00012(760 –ρ)(273 + t _р).                            (9.1)

 

A flash point determined according to standard procedures in both open and closed crucibles. The difference between the flash point, determined in open and closed, is 20... 60 °C. In closed crucibles vapors generated by heating the liquid fuel, are not removed to the surrounding space. The concentration of fuel vapor mixed with air at which the flare is achieved by heating a lower temperature than in open crucibles. At low temperature liquid fuels flash determine it’s normally closed, and at high - in open crucibles. The flash point of fuel oil of different brands should not be below 80 – 140 °C.

 

Description of laboratory installation

 

And flash ignition temperature is determined in the outdoor unit. An open-type device consists of the metal crucible diameter of 64 ± 1 mm, a height of 47 ± 1 mm and placed in a sand bath electric heating 2 (Fig. 9.1).

Fig. 9.1. Apparatus for determining the flash point and ignition of liquid fuel:

1 –metal crucible; 2 – steel sand bath with electric heating;
3 – thermometer; 4 – movable foot

3 is a thermometer for measuring the temperature of the liquid fuel, the upper end of which is fixed to the tripod by means of movable legs 4. The lower end of the thermometer is immersed in liquid fuel. Heating of a sand bath 2 is made with an electric heater, which turning on by two buttons on the instrument panel. Power of electric heating is selected by including the appropriate button 150 or 250 watts.

Order of work realization

 

Beforehand wash with petrol and place the preheated crucible 1 in a sand bath 2 so that the level of sand is the same height as the level of fuel in the crucible. Then reinforce the tripod foot 4 with thermometer 3 at such a height that the mercury bulb of the thermometer is placed in the middle between the bottom of the crucible and the liquid level. When testing a flash of liquid fuel up to 210 °C, the liquid level must be at a distance of 12 mm from the edge of the crucible.

Turn on the electric heating sand bath. Initially, the speed product temperature of 10 °C/min, and then 40 °C to the expected temperature of the flash 4 °C/min. Over 10 °C before the outbreak of expected temperatures begin every 2 second to test the flash, spending on the edge parallel to the surface of the crucible fuel the flames of incendiary device. This makes two turnovers: one clockwise, the other – against. The duration of the test shall be no more than 2 – 3. The moment of the appearance of the flash of blue flame liquid fuel, usually accompanied by a slight explosion, in which noted the appearance and run fast disappearing blue flame. For flash point thermometer indication should be taken at the time of the outbreak. Allowable discrepancy between two parallel definitions for liquid fuel with a flash point above 150 °C is in the range of 6 °C.

The temperature of the liquid fuel ignition is determined after the establishment of the flash point. For this purpose, the liquid fuel heating continued at 4 °C/min. Every 2 °C temperature rise fire incendiary devices carried horizontally above the surface of the crucible. The temperature at which the liquid fuel is ignited and remains lit for at least 5 seconds, is the ignition temperature. After the fuel ignition weakens the foot tripod and the crucible is removed from the thermometer. The crucible is covered with a lid to stop the access of air.

Permissible divergence between the two definitions, the ignition temperature is 6 °C. After determining the ignition temperature of the sand bath was stopped heating. By reducing the temperature of the liquid fuel in the 40 °C heat renew the sand bath and the test is conducted for the second time.

Processing of results

 

Flash point and ignition of the liquid fuel is determined with an accuracy of 1 °C using a thermometer. Air pressure in the experimental conditions measures according to the barometer.

Calculate flash point under normal pressure t₇₆₀ by the empirical formula (9.1). Data should be recorded in the table (Table. 9.1).

Determine the difference between the obtained characteristics of the liquid fuel.

Table 9.1

The experimental values ​​ of the flash point and ignition

Temperature, °С	Experiment		Variation
	1	2
Flash Flashes under normal conditions Ignition

 

 

Laboratory work 10

Laboratory work 9

Study of characteristics of fire hazard

 

Objective: learning the basic indicators of fire and explosion hazards of substances and materials, types of combustion, methods for assessing the explosion and fire objects and procedure of determining the flash point and ignition of the liquid fuel.