6 BULLETIN 379, U. S. DEPARTMENT OF AGRICULTURE. 
Early results prior to the opening of the threshing season indicated 
that opinion as to the cause of explosions and fires of this nature was 
divided between natural causes and incendiarism. The principal 
reason advanced for this latter conclusion was that prior to the 1914 
season explosions were not very frequent. This led to the conclusion 
that means were being taken maliciously to destroy the separators by 
introducing matches and explosives into the grain bundles. 
The following summary indicates the local opinion advanced as to 
the causes of 121 explosions personally investigated during the 1915 
season: 
Matches, incendiary, and _  acci- Crowding: machine 2 =e 1 
gemtat 2 a eee ee 60 
Not given, and indefinite_________ 14 121 
Foreign material, sparks from 
RANaN S22 na ae ~14 PAS 
Se eS = Believed to be incendiary________ 49 
Siac, electricity = = ae 10. gration makerials eee eee Wi 
Powder or explosives______-___-__ A Sine: SSS ; 1 
Engine sparks ————————— 2 Statice electricity____ Se SRD 
Belge Spikes. 5. 2 ee ae eee NOL piven: Dons 2 ee 11 
ETO PORES a es wire eS eee i 
Tn connection with obtaining the opinions of the local thresher men 
and the grain owners, a special effort also was made to secure any 
evidence sustaining the conclusions advanced. In the great majority 
of cases there was no definite reason for supporting the conclusion 
which was based frequently on current rumors. In some cases, how- 
ever, matches were found in the grain pan, but it was impossible to 
determine whether they had fallen into the machines accidentally 
or had been introduced intentionally. 
RESULTS OF FIELD INVESTIGATION. 
SUMMARY OF INVESTIGATORS’ OPINIONS. 
In each explosion and fire the investigator summarized the evi- 
dence obtainable, and after careful consideration of all information 
available assigned the cause most probable in his opinion. The 
following summary shows the conclusions reached in 94 special cases 
investigated : 
Wiatie “CleClLricity 2 Te ae 45) Incendiary. > ae eee 1 
Smut explosion ene _. -25 | Beater striking conveyor=] == 1 
Friction sparks_ u 80 | ING clue: ee eee eee 1 
Matches___ = “47 hh eS eet 
Doubtful ____ 2 oie Saeed o eee ss 94 
Teeth striking__ pf ie ete 1 
About 75 per cent of the occurrences were assigned to the presence 
of static electricity and to smut explosions. The percentage assigned 
