Why must you carry out the oxidation of cu with hno3 in a fume hood?

The reaction produces hydrogen gas, which is dangerously explosive when mixed with oxygen.

The reaction is a metal-acid reaction, where a salt, copper nitrate, and hydrogen gas is produced. The reaction equation is:

Cu + 2HNO₃ → Cu (NO₃) ₂ + H₂ (g)

Hydrogen gas is a very explosive gas so it requires a fume hood for effective disposal and prevention of buildup