230VAC Triac snubber resistor arcing
When your resistor starts spitting out flames, it means the voltage across the resistor exceeded the maximum rated voltage and/or over heating. I'm guessing you're using 0603 resistors which means the peak voltage across the  snubber resistor is exceeding the 75V rating. The snubber resistor will see the peak voltage of your input voltage. I would use a ceramic carbon resistor (Ohmite OX &amp; OY series) for your snubber resistor since they can handle high joule loads. There are MELF film resistors made by Vishay (CMB series) that can handle pulse loads.
You have another problem. C4 &amp; C1, in conjunction with L1, is causing ringing on the output. This causes ringing peaks about 2x the peak voltage on the output. You need to de-Q the inductor by placing a resistor across the inductor (around 10  ohms).
This circuit is easy to simulate in Spice. You can use a switch component for your triac to simplify things.