Optimal way to check repeatedly close objects

Hi, I am developing simple flammable object. I have made it but i am having second thoughts on implementation. I have flammable object that can catch fire.Every flammable object that is on fire cast every 0.1sec OverlapCircleAll to check its surroundings for other flammable objects so it can fire them up. This works well on static and dynamic moving objects.

It works fine but I am having second thoughts about performance impact on lets say 100 objects casting OverlapCircleAll. Any ideas to improve performance or I should not bother ? Thanks.