There's little concern. Temps of 30* isn't going to lower the surface temps of the body temperature of the chicken to frostbite. As stated well above, the frostbite is normally the result of too high humidity that condensates into frost. Think of old refrigerators that you had to manually defrost, back in the day.
We have had months of sub-zero weather. We haven't seen daytime highs above 25*, consistently, for two months. They hens are fine and laying up a storm. No worries and no heat lamps or artificial heat either. Chickens have been raised in the northern Europe, Canada and the US for centuries.