A garage that specializes in foreign cars had a small magnesium fire when a car part was ignited. The mechanic knew from his training that he should not use water but could use a dry powder like a sodium chloride based fire extinguishing powder (MET-L-X) or a graphite based (LITH-X). He knows that the CO2 extinguishing powder is not a good choice.

1. Explain the reasons why the mechanic thinks using CO2 is not a good idea.

2. If MET-L-X or LITH-X is used, a residue could be left on the metal and if cleaned with water, the fire may be rekindled. Explain the chemical process involved in this phenomenon