Incomplete combustion happens when there isn't enough oxygen for a fuel to burn completely. This can create some serious safety issues. Here are the main things you should know:

1. Toxic Gases: When fuel doesn’t burn all the way, it can produce carbon monoxide (CO). This gas is colorless and has no smell, but it is very dangerous. Even a little bit can make you sick, and it can be deadly.

2. Wasted Energy: Incomplete combustion means that the fuel isn’t used up completely. This leads to wasted energy and higher costs for fuel. It can also create soot and other stuff that can damage appliances and vehicles.

3. Fire Risks: When there’s unburned fuel around, it can increase the chances of a fire. This fuel can build up and might catch fire under certain conditions.

4. Environmental Effects: Incomplete combustion can release harmful particles and other pollutants into the air. This is bad for air quality and can harm the environment.

It’s really important to understand these risks when working with combustion. Remember, safety comes first!