hook.Add( "EntityTakeDamage", "EntityDamageExample", function( target, dmginfo )
    if ( target:IsPlayer() and                                          -- only checking players
    table.HasValue({TEAM_GASMASK,TEAM_OTHERGASMASK},target:Team()) and  -- enter jobs here
    dmginfo:IsDamageType(1048576)                                       -- find the numbers here: https://wiki.facepunch.com/gmod/Enums/DMG
    ) then
        return true                                                     -- try only "return" if that fails or "return false"
    end
end )