I've Heard Catalytic Converters Are Dangerous, Is This True?

Catalytic converters are not dangerous per se and they do help to significantly reduce the level of greenhouse gas emissions from car exhausts. So they are not dangerous in normal operation and are, in fact, good for the environment albeit at the expense of some engine performance in that they slow the exit of exhaust gases from the system.

However, what you are probably referring to is the working temperature of a catalytic converter. The working temperature varies from vehicle to vehicle but is usually in the order of several hundred degrees, significantly higher than the normal working temperature of the rest of the exhaust system.

Apart from the possibility of burning yourself badly if working under a car with a hot exhaust, the main danger lies during the summer when parking a vehicle over flammable materials such as long dry grass, which could easily ignite by coming into contact with the converter. On 4 x 4 vehicles, this is also a real possibility when off-roading as grass can become entangled in the exhaust system and be set alight by the catalytic converter.