With no let-up in pollution by ash let loose after burning rice husk by industrial boilers the State Pollution Control Board has served notices on 15 units in the Baddi-Barotiwala-Nalagarh industrial area to switch over to alternative fuels like furnace oil, diesel or petrol for all boiler operations within a month. These units which comprise textile and paper mills have been directed to submit an action plan about switchover to an alternative fuel.