def calculate_common_intervals_helper(intervals1, intervals2):
    """Helper function to calculate_common_intervals used to calculate the intersecting intervals
    between two lists of intervals.

    Args:
        intervals1 (list):  A list of TimeIntervals
        intervals2 (list):  A list of TimeIntervals

    Returns:
        A list of TimeIntervals common to both the supplied intervals.
    """
    common_intervals = []
    for interval1 in intervals1:
        for interval2 in intervals2:
            intersection = interval1.intersection(interval2)
            if intersection:
                common_intervals.append(intersection)

    return common_intervals