Extension cord and fire hazard

[Stevey87]

I have a coralife timer connected to each socket on a wall. Each timer has 8 sockets and most of them are plugged; 2 heaters, 5 wave makers, lights, protein skimmer, etc. My dad just told me don't plug in a room heater (not aquarium heater) to an extension cord or cuz if I do I will get fire. I've read stories of people's power cords burning and causing big fire but no ones knows for sure if it's cuz of too many cords or salt water dripping. I'm worried about lights plugged in mostly because 150W MH and total of 96W T5HO together or one for each socket is too much, along with other cords for wavemakers and such. What do you think? Am I worrying too much or is it legitimate concern?

I also got computers and other stuff connected to other sockets throughout the room.