The light on my ceiling was pre-wired for a fan (separate switch for fan and light), but the ceiling electrical box is plastic. The instructions that came with the fan I bought state "never use a plastic box, use fan approved metal only or you will die a horrible death and your estate won't be able to sue us, ha!). What are the chances that this fan will fall on mt head? I've seen fan-approved plastic boxes at Lowes, Home Depot, etc. How can I tell if I have one? Thanks, John