NEVER enter a gas site that has ‘Ordinary’ in its name, as you learned the hard way you will get blown up by sentry guns.
You might be able to get those out of the way with a big enough ship, although I’m not sure whether they will respawn. In gas sites you just scanned down powerful Sleeper NPCs will spawn in 15-20 minutes and if you are not in a battleship or something you will get blown up, although they spawn 50km away and you have enough time to stop your gas harvesters (if you leave without stopping them you will lose the gas you were harvesting in that cycle) and get out of there.
there is still few incorrect in gas sites, but not critical. for example: all abilities of sleepers, like scram, neut or web are activating not in 70, 40 or 30km, but 69.999, 39,999 or 29,999km. its important if you need keep range.
thx for your job anyway.