Yeah, I don't agree with AH's take either, I'd still give Zippo 6 dice to resist.
Impact armor is halved for elemental effects merely to deal with the fact that a flak vest is
really good at protecting you from being shot (8 armor!) not so good at keeping you from being stabbed (6 armor!) and downright awful (but not entirely useless) when being set on fire, electrocuted, or immersed in acid (3 armor).
"Fire Armor" is better than Impact armor for protecting you from fire (duh) therefore is not halved, but does jack diddly against electricity and acid.
Impact armor is the generic "catch all" solution that allows sheer bulk to protect you from the worst of an attack, it's not geared towards being
good at it, it just
helps, therefore its value is halved against elemental attacks (elemental attacks do not have "armor penetration: half"* they simply are resisted with
half impact).
*How do we know this? Because all of the damage types are listed under "see page 154" where Electric (also fire, acid, cold, fatigue, and falling continuing onto page 155) says "resisted with half impact." It is not an armor modifier.
QUOTE
Certain environmental effects—acid, fire, extreme cold,
electricity—have a slightly different effect than standard types of
damage, as noted below.
Acid damage is treated as Physical damage
and resisted with half Impact armor (rounded up).
Cold damage is treated as Physical
damage and resisted with half Impact armor (rounded up).
Electrical damage is treated as Stun damage and resisted
with half Impact armor (rounded up)—metallic armor, however,
offers no protection.
Falling Damage
Use Body + half the rating of the
character’s Impact armor (round down) to resist this damage.
Fatigue Damage
this damage cannot be resisted.
Treat Fire damage as Physical damage, but Impact armor only
protects against it with half its value (round up).
Note how none of them say that the damage has
armor penetration but that a
damage resistance test is made using some value (typically half the target's impact armor).