import math


def newmark_overpressure(energy_mttnt, radius_m):
    """
    Newmark-Hansen Overpressure formula.  Intended for surface blasts, but adapted to air-bursts.
    :param energy_mttnt: Energy in Megatons TNT
    :param radius_m: Actual distance from blast in m (hypotenuse distance for airburst events).
    :returns: overpressure in bar
    :Reference: NuclearBlastOverpressure.pdf, Equation 3
    """

    energy_tnt = energy_mttnt * 1000000
    return (6784 * (energy_tnt / (radius_m ** 3))) + (93 * (math.sqrt(energy_tnt / (radius_m ** 3))))