The purpose of this letter is to provide all federal explosives licensees and permittees guidance on the safe storage of explosive materials. Electronic nicotine delivery systems, or other similar devices, are electronic devices that, through an aerosolized solution, deliver nicotine, flavor, and/or other substances (including non-tobacco products) to the user inhaling from the device. ATF has determined that electronic nicotine delivery systems are spark producing devices. Therefore, they cannot be brought into or within 50 feet of any outdoor explosives storage magazine or within any room containing an indoor magazine.