Barium hydroxide lime is not used as carbon dioxide absorbent in circle system, because:
Soda lime is the more common absorbent and is capable of absorbing up to 23 L of CO2 per 100 g of absorbent. It consists primarily of calcium hydroxide (80%), along with sodium hydroxide, water, and a small amount of potassium hydroxide. Another absorbent, barium hydroxide lime, is no longer used due to the possible increased hazard of fire in the breathing system. Ref: Butterwoh IV J.F., Butterwoh IV J.F., Mackey D.C., Wasnick J.D., Mackey D.C., Wasnick J.D. (2013). Chapter 3. Breathing Systems. In J.F. Butterwoh IV, J.F. Butterwoh IV, D.C. Mackey, J.D. Wasnick, D.C. Mackey, J.D. Wasnick (Eds), Morgan & Mikhail's Clinical Anesthesiology, 5e.
Because of its lesser absorptive capacity
Production of poisonous gases
Increased hazard of fire in the breathing system
Because of its method of hardness