About as safe as any other use of a motor. Moving parts like belts and fans are potentially a problem. The engine won't come apart in a dangerous way. It might

About as safe as any other use of a motor. Moving parts like belts and fans are potentially a problem. The engine won't come apart in a dangerous way. It might overheat, which creates superheated water in the cooling system, which is designed to handle that. Although I sort of doubt it since they are basically using about 1/20th of its maximum power output. The most dangerous thing about this is likely the standard risks of any generator, fuel and electricity.