well I have a homemade Gravity bong that uses a Gatorade bottle and a metal bowl that I bought. Absolutly 100% known to me that no plastic gets burned. I'm pretty sure that if there was a natural reaction to it or poisoness smoke and what not I would have felt the effects of it after a year of taking hits from this grav bong. I do track at school and my lungs work fine lol. so yeah.

So imo I dunno what the whole plastic is dangerous thing is about anyway.