(b)the behaviour or a reasonable apprehension of the behaviour of the persons employed on any railway, canal or other public work, or in or upon any manufactory or other commercial concern, under construction or in operation at any place necessitates the employment of additional police at such place, the Administrator, or the competent authority, as the case may be, may depute such number of additional police to the said place for so long as the necessity to employ the additional police shall appear to the Administrator or the competent authority to continue.