Trichloroethylene is a long word that means a special kind of chemical. It looks like water that has been turned into a gas, but it can make you very sick if you breathe too much of it in.
People use trichloroethylene to clean things like metal machines and electric parts because it is really good at getting rid of dirt and other things that don't belong there. It's even used to take off stubborn stains like bicycle chain grease.
However, since trichloroethylene is so strong, it needs to be handled very carefully. People who work with trichloroethylene have to wear special clothes and masks to make sure they don't breathe it in or get it on their skin.
When we are around trichloroethylene, our bodies can take in the chemical, which can make us feel tired or dizzy. Some people can even get very sick if they breathe in too much. That's why adults and scientists are very careful about how they use and talk about trichloroethylene, because they want to keep everyone safe!