A crowbar can be a very useful tool if you have forgotten the key to a lock or even lost it. With the correct application of pressure, you can use a crowbar to quickly break a lock and solve your problem.
Step 1 - Position
Get yourself into a good steady position. Spread your feet shoulder-width apart and slightly bend your knees. A strong base is important because you will need to stay still in order to apply all of the pressure through the crowbar. Also, make sure you are close to the lock so it's easy to access.
Step 2 - Wedge
Wedge the crowbar into a spot where it will push the lock out towards you. Do not worry about damage because, by this stage, you won't have any alternative! Make sure the crowbar is in place by applying a small amount of pressure. Watch to check the lock buckles forward slightly.
Step 3 - Break Lock
With the crowbar wedged in, apply all of your force down or through the crowbar, pushing away from you. This should create major pressure on the lock, and it will either snap or break. Make sure you wear safety goggles to protect yourself from flying pieces of debris.