[bronson] the HALIFAX EXPLOSION 33 



Dalhousie University Science Building, about 3,500 meters from 

 the explosion. I first felt a shaking of the building no greater than 

 that caused by heavy blasting in the railroad cut, but it seemed to be 

 directly under the building and I started for the boiler room, fearing 

 an explosion there. I had gone less than 30 feet when the crash came 

 which completely destroyed the windows and sashes on three sides of 

 the building, broke heavy doors and locks, and even shifted partitions. 

 The comparatively slight earth shock can be explained by the fact that 

 the explosion was practically on the water, even though the ship was 

 touching ground. Unfortunately I find it difficult to make any 

 satisfactory estimate of the time between the arrival of the two shocks, 

 but should estimate it between 6 and 10 seconds, which would not in- 

 dicate a very high velocity for the air wave, or explosion impulse as it 

 is generally called. 



1 1 is a well-established fact that the velocity of the explosion impulse 

 is much greater than the normal velocity of sound. The wave probably 

 starts out with about the same velocity as that of the detonation of the 

 explosive, which may be above 5,000 meters per sec. The velocity 

 decreases very rapidly with the distance, especially at first, and is 

 said to reach the normal velocity of sound at about the distance that 

 windows cease to be broken. The velocity at any distance apparently 

 depends both on the quantity and nature of the explosive, though the 

 initial velocity seems to be independent of the quantity. All three 

 of the above explosives, and especially picric acid, have exceedingly 

 high detonation velocities. The terrible destruction caused by the 

 air concussion was undoubtedly due to this intense compression 

 impulse travelling with high velocity. 



Whether the above correctly interprets the phenomena or not, 

 there is no question about the terrible destructive effect of the explosion 

 impulse. In a general way it can be said that buildings within a 

 radius of half a mile of the explosion were totally destroyed and that 

 up to one mile they were very largely rendered uninhabitable and 

 dangerous. No section of Halifax city escaped serious damage to 

 doors, windows and plaster. The damage to the Dalhousie Science 

 Building, already referred to, was quite characteristic of those sections 

 of the city farthest from the explosion. More or less severe damage 

 was caused as far away as Sackville and Windsor Junction, 9 or 10 

 miles N.E. of the explosion, and for a similar distance in the opposite 

 direction. At Truro, 62 miles, and New Glasgow, 78 miles, the 

 shock was sufficient to jar buildings very appreciably, and even to 

 shake articles off from shelves. Even as far away as Charlotte town, 

 135 miles, and North Cape Breton, 225 miles, the explosion was 

 distinctly felt or heard. 



Sec. Ill, Sig. 3 



