THE PLACE OF NIGHT WORK IN INDUSTRY 
OR the purpose of the investigation, night work is 
defined as operations conducted by a separate group of 
employees whose hours of work commence after the day 
force has terminated its work period. It doesnot thereforein- 
clude overtime work, because in this case the same group of em- 
ployees work the regularly scheduled hours and continue at 
their post for an additional, usually indefinite, period of time. 
Night work, on the other hand, is done by laborers who are 
hired specifically for such work or are transferred to this force 
from day work and whose hours of work are generally fixed in 
accordance with a predetermined schedule. Where night 
work occurs, it may be found in plants which operate con- 
tinuously for a part of or throughout the year, or where the 
operation is non-continuous, with a break between the shifts. 
The greatest number of night workers are engaged in indus- 
tries which are continuously operative. 
The continuous industries may be broadly defined as those 
which are run during the entire 24 hours, because the process, 
the heavy overhead, the expense of starting and stopping 
operations, or the public service require it. Production may 
be absolutely continuous or it may be so for five or six days 
with a pause at the week-end. In the report, entitled “The 
Twelve-Hour Shift in Industry,” of the Committee on Work- 
Periods in Continuous Industry of the Federated American 
Engineering Societies, about forty leading continuous indus. 
tries are listed as follows: 
|. Heat Process Industries—Iron and steel, copper, zinc, 
lead, nickel, aluminum, flint glass, bottles, window-glass, 
plate glass, portland cement, lime, brick, pottery.! 
Chemical Industries—Heavy chemicals, fertilizers, ex- 
plosives, dyes, industrial alcohol, wood distillation, 
1 Only 29% or 3% of employees are shift workers. 
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