(n.) A U.L. rating given to a container where the door has been tested against forcible entry with common hand tools and/or abrasive cutting wheels, power saws, and oxy-fuel gas cutting or welding torch and may further include nitroglycerin or other high explosives for a period of 60 man minutes. The total quantity of explosives employed may not exceed 8 ounces. Not more than 4 ounces is to be used in a single charge.

Source: Lock Industry Standards and Training (LIST) Council