Are they any boiler men on here or women... by boiler I mean furnace my sister just had some guy out yesterday for it and its still blowing out unburned fuel... he said the water pressure gauge inside is running high it should be around 15lbs of pressure and its at 30... can an oil burner blow up...

I'm not a boiler woman, just have owned them.
There's a pressure relief valve that will leak water if pressure gets too high. It can go higher than 30.
(A boiler boils water for either steam or hot water going to radiators. A furnace heats air for vents.)

She should be on here asking, or she should call the 'guy' who was just there yesterday. It just doesn't translate well second hand.
Although maybe some of the guys here will be able to advise.

If it is "blowing out unburned fuel", your sister needs to get someone, who knows oil burners & boilers, out there proto. If the pressure is too high, it could be a bad expansion tank, faulty reducing valve (aka fill valve), or a leaking domestic coil if the boiler has one.