Motor vehicles are made of metals, plastics and various other materials, which can tear into soft flesh. Up to eleven different fluids, which can be very hot, very cold, poisonous, toxic, acids or alkaline which burn into human tissues. Continuous studies reveal all manner of substances that are carcinogenic, so proper precautions need to be taken to avoid harmful materials. This can be in the form of proper ventilation, protective clothing, appropriate safety equipment and up to date knowledge of relevant safety data on the materials your handling. These are often marked clearly on the containers these days, if you are unsure of the material you are handling, then don't handle it until you are sure it is safe.
Secure any loose clothing which could drag you into moving machinery.
Electric cooling fans can switch on and cut into flesh even when the ignition keys are removed, catching unwary soles who reach down around fans thinking that if the engine isn't running that it is safe.
When the engine is running, rotating components may appear to be invisible, and are capable of amputating misplaced fingers etc. Those rotating parts also catch loose clothing, winding it around and around until it tears away the clothing or tears away the limb. If say, a loose neck tie was to catch in the fan, it would quickly wrap around the pulley, choking the wearer, even if you neck was strong enough to stall the engine, you would still not be able to release the tie or turn the engine backwards to release it in time and you would choke.
Many of the liquids used in motor vehicles can damage clothing, in the case of battery acid it can burn straight though most clothing, then it starts on your skin.
Skin is water proofing for your body, however petroleum products such as petrol, oils, and greases are not water based. Many people with sensitive skin have a strong reaction to petroleum products like petrol and grease, their skin flares in an angry, stinging rash called 'dermatitis' which can take months to heal. Those who are not as susceptible to 'dermatitis' continue to expose themselves to petroleum products and risk blood poisoning. The petroleum products act as a solvent, and melt away the body's natural oils, seeping deep into the skin, where it finds it's way into the bloodstream. Spilt petrol can be under pressure, and spray many meters from a leaking joint or hose, and then there is a real risk of a fire starting, when petrol contacts hot engine parts, electrical parts or the hot exhaust system.
Motor cars have complex electrical systems, which range in voltage from mere millivolts to nearly one hundred thousand volts in the spark plug circuit. Your body can carry static electricity that can set off SRS Air Bag Systems, damage computer components and set computer codes. Ignition systems can develop enough voltage to shock your nervous system and your heart muscles. I personally haven't heard of anyone dying from a spark plug, but when you get caught you don't just suffer the shock, you pull away in shock and usually damage yourself by striking a limb against the car body. As well as high voltages, there is a high risk of fire if wiring is shorted to ground by an object such as a dropped spanner. Once the object lodges against the wiring it gets hot from the discharging battery and welds itself in place, see section about 'Fire' .
Tremendous amounts of heat are generated in motor vehicles. Both petrol and electricity can start and continue to feed a fire should one start, take adequate precautions. Heat is created, radiated, conducted, dissipated, transferred, and expelled. Sometimes components can get hotter after the vehicle is turned off because the components cooling system is turned off when the engine is stopped, sometimes cooling system fans will turn themselves back on long after the engine has been switched off, see section on 'Moving parts'back
When starting a vehicle make sure the handbrake is applied and your foot is firmly on the footbrake, and the vehicle in out of gear in neutral or park. Many motor mechanics have been driven over or pinned against a bench or dragged down the road caught in the doorway of a vehicle which started in gear, or slipped into gear as the vehicle started. Use good strong wheel chocks each side of the wheels to prevent vehicle movement. Faulty or broken engine mountings or transmission mountings can allow enough movement of the gearbox to pull the car into gear, when the engine is running, this has been the cause of many aviodable accidents.
Always use properly positioned axle jack stands, and a suitable jack when lifting a vehicle off the ground. The car jack in the boot was only designed to lift one corner of the car off the ground to change a flat tyre. Do not use it to lift a car off the ground for servicing or repair.