Which precaution is advised when using osmium tetroxide as a fixative?

• A. Use under a chemical hood due to its volatility
• B. It can be handled openly in a well-ventilated room
• C. It should be warmed to accelerate fixation
• D. It should be kept in direct sunlight to preserve activity

Answer: (A)

Osmium tetroxide is extremely volatile and highly toxic, with vapors that readily escape into the workspace and can irritate or damage the eyes, nose, throat, and lungs. Because of this, it must be used in a chemical fume hood that actively exhausts vapors away from the operator, providing the necessary containment and protection. Handling it openly in a well-ventilated room would expose personnel to dangerous vapors despite any general ventilation. Warming the fixative would increase vapor release and hazard, not improve safety. Keeping it in direct sunlight is unsafe and irrelevant to preserving its activity. The fume hood is the appropriate precaution to minimize inhalation exposure and ensure safe handling.