At first I burn almost all transistor after power on, then I test lower voltage than 36V like for previously tested BD243.

FZT851 at 12V without LED:

• no heating
• 0.2W consumption
• 0,017A
• tube glow 1-2cm above board
• no visible sparks
• when you touch board, current go transistor deathly values

FZT851 at 12V with red LED:

• no heating
• 0.2W consumption
• 0,2A
• tube glow 3cm above board, 
• visible sparks if I scratch with tube wires over board
• when you touch board, current go transistor deathly values

RESULT:

Subjective I think, I have almost same results with FZT851 at 12V like BD243 at 36V

FZT851 is SMD in SOT223 package, is more sensitive and is harder for cooling.

You can see some neon glow on 5-6V.