(b)that 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 Government or the competent authority may depute such additional police to the said place as it shall think fit and keep the said Police employed at such place for so long as such necessity shall appear to it to continue.