May ignite on exposure to air, particularly when containing adsorbed hydrogen; readily causes ignition of flammable solvents in the presence of air.

Very little information is available on the toxicity of palladium and its compounds. There is some evidence that chronic exposure to palladium particles in dust can have toxic effects on the blood and respiratory systems. Finely divided carbon is irritating to mucous membranes and the upper respiratory tract.

Palladium on carbon catalysts containing adsorbed hydrogen are pyrophoric, particularly when dry and at elevated temperatures. Palladium on carbon catalysts prepared by formaldehyde reduction are less pyrophoric than those reduced with hydrogen. Finely divided carbon, like most materials in powder form, is capable of creating a dust explosion.

Catalysts prepared on high surface area supports are highly active and readily cause ignition of hydrogen/air and solvent/air mixtures. Methanol is notable for easy ignition because of its high volatility. Addition of catalyst to a tetrahydroborate solution may cause ignition of liberated hydrogen.

Because of its high potential for ignition, palladium on carbon should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with reactive and explosive chemicals (Chapter 5.G). In particular, palladium on carbon should always be handled under an inert atmosphere (preferably argon), and reaction vessels should be flushed with inert gas before the catalyst is added. Dry catalyst should never be added to an organic solvent in the presence of air. Palladium on carbon recovered from catalytic hydrogenation reactions by filtration requires careful handling because it is usually saturated with hydrogen and will ignite spontaneously on exposure to air. The filter cake should never be allowed to dry, and the moist material should be added to a large quantity of water and disposed of properly.