A video went around a while ago of a helicopter fire fighting display. The pilot had difficulty putting it out, but the video clearly showed the downwash making things worse.
That's just one study. I agree that what Dave said is possible. I've never done any fire fighting, but have spoken briefly to someone who teaches it and there's definately a lot to know about fires, fuels and techniques.
As far as disk loading, if a higher downwash velocity is a problem and transit speeds aren't a concern go with low disk loading. It won't change the total energy in the air (that's mass dependant only), but it will slow it down.