FIREWORKS

128 Fireworks Principles and Practice
Table 5.1 Standard Sieves
American Sieves British Sieves Sieve Opening in Micron
12
18
20
30
35
40
60
70
80
100
120
140
170
200
230
270
10
16
18
25
30
36
60
72
85
100
120
150
170
200
240
300
1680
1000
840
590
500
420
250
210
177
149
125
105
88
74
62
53
place in confinement. In an enclosed space the combustion rate rises
quickly and may become explosive.
Turning to the important matter of sensitivity, the firework maker
is primarily concerned with the sensitivity to shock and friction. To
some extent he is also concerned about ignition temperature, but the
sensitivity to shock and friction is of greater practical importance,
mainly because firework mixtures are usually more sensitive than ordinance
compositions. In general firework mixtures which are more sensitive
to friction are also more sensitive to shock, but this is not necessarily
the case.
Shock sensitivity is usually determined with a drop hammer. A small
quantity of composition is placed on the anvil of the apparatus and a
known weight is allowed to fall on the anvil. The weight is dropped
from various measured heights until a minimum distance can be
recorded at which the material explodes. Several trials are necessary for
any degree of accuracy, but the method provides a useful comparison
between various mixtures. Sensitivity ratings can be produced in this
way, one method, for instance, uses picric acid as a standard with a
figure of 100.
Friction sensitivity is sometimes vaguely determined by striking the
mixture a light glancing blow with a polished hardwood mallet, but a
more accurate method uses two weighted porcelain plates. A small