Oxygen bomb calorimeter instrument in the ignition wire is easy to burn out but sample coal not burn what reason be

First, calorimetry (kcal / calorimeter instrument) oxygen bomb ignition wire (nichrome wire wire material is good \ combustion)?
Second, check the calorimeter oxygen bomb is sufficient oxygen?
Third, oxygen bomb is leaking (usually seal ring)
Fourth, samples (coal samples / standard sample / standard material, etc.) have been dry air? Wet and easy to burn is not enough, samples (coal samples / standard sample / standard material, etc.) after sampling directly with a drying oven drying!
Fifth, calorimetry (kcal / calorimeter instrument) oxygen bomb ignition wire (nichrome wire wire and sample \ combustion) (coal sample / standard / standard substances) contact? Need the ignition wire (nichrome wire burning \ \ complete contact samples)!
Sixth, the voltage is too high? High ignition oxygen bomb calorimeter (wire nichrome wire \ burning wire is easy to break).

Seventh, the sample (coal sample / standard / standard substances) probably because of low calorific value (this is rarely higher than 200 kcal, will be successful, if the sample (coal) / sample) to low calorific value of additives, such as benzoic acid mixed with a certain quality of the calorific value of combustibles.