Hydrogen peroxide when mixed with acid for etching pcb or other usage, gives away very nasty fumes. these fumes are toxic, can cause serious damage to lungs if directly inhaled even for short period of time. These fumes when enter in lungs, can cause wounds in trachea and damage to bronchioles. ultimaletly resulting in serious infections and respiratory disorders.
So. the process involving the usage of acid in any way that can produce fumes should be carried out in a well ventilated place. Always use protective eyewears, mask, hand gloves, protective clothing,and take necessary precautions.
good luck.