From the Epic Armageddon files once hosted on the GW website:
Epic Armageddon Ch 5, Pg 102, Sidebar 5.4.1: Imperial Void Shields
Imperial Titans are protected by void shield
generators. The number of void shields each
Titan has is noted on the Titan’s datasheet.
Each void shield will automatically stop one
point of damage and then go down. Do not
make armour saves for damage stopped by
void shields, nor allocate Blast markers. Once
all of the shields have been knocked down, the
Titan may be damaged normally and you may
make saving throws against any hits that are
scored. Hits from close combat ignore void
shields but units using their firefight values
must first knock down any shields before they
can damage the Titan.
Void shields that have been knocked down can
be repaired. Each Titan can repair one downed
void shield in the end phase of each turn. In
addition, if a Titan regroups it can use the dice
roll to either repair the void shield or remove
Blast markers (eg, if you rolled a 2 you could
repair 2 shields, remove 2 Blast markers or
repair 1 shield and remove 1 Blast marker).