The civil and criminal liabilities imposed by sections 71-1929 and 71-1933 of this title upon persons violating the provisions of titles 1 through 11 inclusive and title 19 of article 17 and by sections 71-1929 and 71-1933 of this title shall not be construed to include any violation which was caused by an act of God, war, strike, riot or other catastrophe as to which negligence or willful misconduct on the part of such person was not the proximate cause.