Don't run an engine in a garage or anywhere else without proper ventilation - EVER! Carbon monoxide is poisonous; it takes a long time to leave the human body and you can build up a deadly supply of it in your system by simply breathing in a little every day. You may not realize you are slowly poisoning yourself. Always use power vents, windows, fans or open the garage doors.
Carbon monoxide is odorless and colorless. Your senses cannot detect its presence. Early symptoms of monoxide poisoning include headache, irritability, improper vision (blurred or hard to focus) and/or drowsiness. When you notice any of these symptoms in yourself or your helpers, stop working immediately and get to fresh, outside air. Ventilate the work area thoroughly before returning to the car.
Don't work around moving parts while wearing a necktie or other loose clothing. Short sleeves are much safer than long, loose sleeves; hard-toed shoes with neoprene soles protect your feet and give a better grip on slippery surface. Jewelry (watches, fancy belt buckles, beads or body adornment of any kind) is not safe working around a car. Long hair should be hidden under a hat or cap.
Don't use pockets for toolboxes. A fall or bump can drive a screwdriver deep into your body. Even a wiping cloth hanging from the back pocket can wrap around a spinning shaft or fan.
Don't smoke when working around gasoline, cleaning solvent or other flammable material. Assume that all liquids and sprays are flammable unless specifically labeled otherwise.
Don't disconnect either terminal from the battery while the engine is running. Modern cars contain many solid-state components and "black-box" computers. You will not get a second chance with solid-state failures; you will get to buy some very expensive replacement parts.
Don't smoke when working around the battery. When the battery is being charged, it gives off explosive hydrogen gas.
Don't use gasoline, kerosene or solvents to wash your hands; there are excellent soaps available. Gasoline contains lead, and lead can enter the body through a cut, accumulating in the body until you are very ill. Gasoline also removes all the natural oils from the skin so that bone-dry hands will suck up oil and grease.
Don't service the air conditioning system unless you are equipped with the necessary tools and training. The refrigerant, R-12, is extremely cold when compressed, and when released into the air will instantly freeze any surface it contacts, including your eyes. Although the refrigerant is normally non-toxic, R-12 becomes a deadly poisonous gas in the presence of an open flame. One good whiff of the vapors from burning refrigerant can be fatal.