Sometimes there are things around us that can be dangerous, like chemicals or sharp objects. Hazards can cause us harm if we aren't careful. Hazard substitution is when we try to make things safer by replacing dangerous things with things that are less likely to hurt us.
Think of it like this: if you have a toy car that has sharp edges, you might swap it for one with smoother edges so that it's less likely to scratch or cut you.
It's like changing the ingredients in a recipe if you're allergic to something. Maybe you can't eat peanuts, so you substitute the peanut butter in a sandwich for something safer, like almond butter.
By swapping out hazards for less dangerous things, we're keeping ourselves and others safe!