You wouldn't really have an issue with the tubing on a bicycle with heat and warping, mainly sheet metal. By the time you could make enough heat to warp a tube you would have had to sit in one spot to long and other damage would be of greater concern. As long as you keep moving as your blasting and not using to harsh of a media you shouldn't have a problem with heat. The biggest problem I see is people using the wrong sand when doing blasting on finer items such as a nice bicycle frame or a piece of aluminum with a lot of detail, myself I always used glass bead in a cabinet and never had issues with damaging what I was stripping including small sheet metal parts from the interior of a truck I restored.
Glenn