Can I use Welder if there are no Fire Energy cards in my hand?
No, you cannot. You must be able to attach at least 1 Fire Energy card in order to use Welder.
Source: TPCi Rules Team (2019-05-09)

Relevant cards

Note: All applicable cards may not be listed below.
SM10_189
SM10_189
SM10_189A
SM10_189A
SM10_214
SM10_214