When fires goes out in the hearth, the indication of all flame indicators is extinguished, the hearth negative pressure i suddenly negative to maximum, the main steam pressure, temperature, flow rate and power load drop rapidly and the negative pressure protective device  acts and alarms. 

The causes of fire going out in boiler hearth are as follows: 

1. The coal quality is poor and the combustion adjustment is not proper. 

2. The boiler operation is under low load, the combustion is not stable and the fuel oil is not used for combustion supporting. 

3. The coal pulverizing system breaks down. 

4. The pulverized coal and coal supply are not uneven, making the flame unstable, or when the blended coal is burnt, the coal is not evenly blended. 

5. The hearth negative pressure is maintained too much. 

6. Due to various reasons, the air supply and pulverized coal supply etc. are interrupted. 

7.If water-cooled wall tube seriously leaks or bursts, a large amount of steam-water will be sprayed into the hearth etc.