Are you aware that if you use a TIG or MIG welder, there is a genuine danger of asphyxiation, if welding in a confined space or an enclosed workshop. This is due to dangerous gases that can be inhaled from the atmosphere.
Argon and CO2 gases are considerably heavy compared to air gases and have a tendency to accumulate near the floor when welding, and build up the more you weld.
Both gases are colourless and odourless and in small concentrations this isn't a serious issue, but when you weld close to the floor, welding under a vehicle or kneeling down, there is a risk you can inhale dangerous amounts of these gases. The accumulation of these gases displaces air and this can suffocate a welder without them having any knowledge.
It is highly advisable to carry out a risk assessment before you weld to determine if you have adequate ventilation to weld.
Another consideration to be aware of is that in an enclosed welding environment gases can accumulate over a period of time. If a gas cylinder valve was to suddenly develop a fault and leak, gas could engulf the enclosed area with unbreathable air.
This is why gas cylinders are subjected to pressure testing regularly. But if a cylinders test date has expired get the cylinder exchanged immediately by your local welding gas supplier.