Soot cleaning does not require professional help, provided you know where to begin. The following cleaning techniques should have your drywall free of soot before you know it.
Step 1 - Setting Up
Before you begin, put on all of your protective clothing, including your respirator mask, rubber gloves and eye protection. Additionally, before you start working you should open all of your windows and doors to ventilate the area around your drywall. If necessary, you can use a fan to help the air circulate.
Step 2 - Use a Dry Chemical Sponge
Start at the top of the dirty area of the drywall and scrub with a dry chemical sponge. Work your way down the section of drywall. Do not worry about removing every last bit of soot yet, as it may not be possible to do this. Be sure that you do not use water during or before this step.
Step 3 - Use TSP Substitute
There are many TSP substitute cleaning products that you can choose from, and their manufacturer's instructions should take precedence over these. However, you should plan to fill a bucket with water and mix in the TSP substitute, then apply the mixture to your drywall using a sponge. Rinse with a second bucket of pure water.
You may choose to paint over your drywall with a coat of primer designed for use with soot damage after this if the problem is still visible.