Wally Bird is correct with regard to proposals for the Avro RJ85 and the MD-87 to be converted for aerial fire fighting. The U.S. Forest Service (USFS) is keen to introduce such smaller jet equipment as air tankers as these aircraft will progressively replace much older prop-driven airplanes. There have been some real problems with the older air tanker fleet over the years in terms of safety. For example, some years ago, the wings came off an elderly C-130 that was being operated by a private company as a fire fighting air tanker while it was making a retardant drop.
I think the Avro RJ85 will face no big problems with regard to being converted to an air tanker role given the success of the BAe 146. And as for the MD-87, it will be interesting to see how this aircraft performs as an air tanker as no one has tried this before with this specific aircraft type.
BTW, back in the day, I oversaw contract helicopter fire fighting operations for the U.S. Forest Service and California Dept. of Forestry. We primarily used twin engine Bell 212 helicopters equipped with either "hover fill" belly tanks or "Bambi" water buckets. This was back when ex-military B-17, B-24 and C-119J fixed wing aircraft were still being used as air tankers.....