def burn_region_is_safe(arr):
    """Check the burn region is dark enough to be outside the fan."""
    h, w = arr.shape
    y2 = min(BURN_REGION_Y + BURN_REGION_H, h)
    x2 = min(BURN_REGION_X + BURN_REGION_W, w)
    region = arr[BURN_REGION_Y:y2, BURN_REGION_X:x2]
    if region.size == 0:
        return False, float("nan")
    mean = float(region.mean())
    return mean <= BRIGHTNESS_SKIP_THRESHOLD, mean