Can you safely saw through a gas pipe?

The gas pipe that leads to the pool heater was capped off inside my house. Now I want to get rid of the pool heater but the pipes are rusted together. PB Blaster did not work. Can I saw through the metal gas pipe that leads to the pool heater? Is it safe? Will the friction cause a heat build-up / explosion (even though the gas supply was capped off)? Will a hand saw or reciprocating saw work?