Many acoustical or popcorn ceilings that were put in, in the 1970's, contained asbestos. If you are unsure about the contents of the ceiling take a piece and put it in a plastic bag and send it to a lab for testing. Once you know that the ceiling is asbestos free and you are ready to take it down, start by turning off the power to the room. Next put down a plastic drop cloth to cover the floor and furniture in the room and protect it from the water that you will be using in this process. Tape plastic over all the outlets and up the walls about 1 foot to keep water from seeping into the walls through the baseboards. Put tape on the walls about a quarter inch from the ceiling as a sealer. Then tape plastic to the tape to protect the walls. Finally roll rosin paper over the floor. This paper will keep the floor from getting slippery, absorb some of the water, and make clean up much easier. Use a garden sprayer and spray a small section of the ceiling at a time and then scrap it off with a wide putty knife. After you've scraped the entire ceiling roll up the plastic inside the rosin paper and dispose of it.