Son Goku was using the Super Saiyan 2 form, and even touching Nova Shenron's body would burn him.
Nova Shenron swung his arm to unleash a scorching blast of wind, and the raging heat wave caused Son Goku to roar as he transformed into Super Saiyan 3 to counter it.
Son Goku met the red palm wind with a punch, but the moment they made contact, the intensely scorching heat wave burned his entire arm.
Chapter 197