PLACE OF NIGHT WORK IN INDUSTRY 9 
throughout the year in industries which operate continu- 
ously without being subjected to seasonal fluctuations, and 
for an indefinite period in plants which are not continuously 
operative. 
FREQUENCY OF ROTATION OF SHIFTS 
The frequency with which the night shifts are rotated, 
where such a policy is in effect, is fairly well standardized in 
each of the industrial groups. For example, in the paper and 
wood pulp, iron and steel and in chemical industries, the 
shifts rotate each week, while in the gas and electric produc- 
tion and distribution and in the petroleum refining industries 
a bi-weekly change is generally in force. Table 2 shows 
the number of plants in specified industries which use the 
weekly, bi-weekly and monthly shift rotation plans. 
TaBLE 2: FREQUENCY OF SHIFT RoTATION 
Number of Plants Using Shift Rotation 
Weal tar Monthly 
Gas and electricity. .....oovvnnnn 
Paper and wood pulp........... 
[ron and steel. ..........ounnn. 
Foundries and machine shops. . .. 
Automobiles. ....vvviiiiiiinaen 
Oi] refining...ovevverenninenenes 
Sugar refining. . “aun E 
Glass. .ocveicevnnnasennnecenns 
Cement, lime, brick, ete.l..... .. 
Mining. susersessarrrvarnree oe 
Chemicals. . . 
Rubber. . 
1 
1 (One plant rotates shifts tri-weekly. 
On the frequency with which night shifts should be rotated, 
the British Committee on Health of Munition Workers in 
1916 reported as follows: 
““ A question of considerable importance in connection with the 
shift system is how long the workers should remain on the night 
shift at any one time. A week is the most common period, more 
particularly where the three-shift system is in vogue. Elsewhere 
the changes are sometimes made fortnightly or monthly, and in 
some instances there is no alternation at all, the workers remain- 
ing continuously on day work, except for occasional changes