I say burn and agree with using silver sulfadiazine until you can get to the vet. Now to correct the issue at hand...how did he get burned?
Did he burn himself while outside his enclosure?
How is he housed? In a tub, aquarium style glass enclosure, or PVC enclosure?
How are you heating the warm side? Under the tank heat mat? Flexwatt? Is it regulated by a thermostat to 90 degrees and monitored with a temp gun or thermometer?
Are there any direct heat sources such as a heat rock or is the heat mat placed inside the enclosure instead of outside and underneath?