Rent or buy a soda blaster or pressure blaster with soda blasting attachment at your local hardware store.
Put on protective clothing, including goggles and mask.
Pour baking soda into tank where indicated, up to fill level.
Following the directions that came with your blaster, turn on air flow.
Turn on blaster nozzle until you can see a steady stream of baking soda flowing out.
Point nozzle at object that needs cleaning, making sure to stay at least a foot away from object.
Move the nozzle in a steady sweeping motion until all paint has been cleaned away.
When finished, turn off blaster and wipe down object; to prevent rusting, leave a small amount of baking soda on metal.