Every bike has the foot standing support. Sometime, it need the welding for joining it other part of bike. So, it is the situation,

1.you need to off the supply of petrol to engine.
2. you need to start the bike upto the consumption of rest petrol in engine.
3. Now, if bike stop and engine is empty from petrol, you have to start your welding work as you are seeing in same video. If there is petrol in engine, then there is the chance of fire of your whole bike with single heat of fire. So, beware from this point.