The holodisk is located in a Average locked safe in Farragut West station. In the room with a locked cage door and ghouls there is a room if you face 180 degrees from the cage door. When you enter the room you will find a computer with options like opening the cage and releasing gas. Behind the desk is the safe containing the note and the laser pistol.
The protocol is probably intended to be an introduction to the laser pistol and its ability to trigger an explosion by igniting gas, as this would be the first place where you can find one if you follow your father to Galaxy News Radio right away.
Congratulations on receiving your new DCTA Standard-Issue Laser Pistol!
Please take a few minutes to go over the guidelines posted in the DCTA Employee Handbook; Section 28.1.1.b, and reprinted below for your convenience.
Section 28.1.1.b - Proper Laser Pistol Usage
It should be noted that all DCTA property should be handled with the utmost care, and used only when necessary. Maintaining personal safety during a Communist attack is a good example of proper usage of your standard issue laser pistol. However, rodent population control is an inappropriate use and subject to disciplinary action, as noted in Section 11.3.5.c.
Section 28.1.1.b.1 - Maintaining Safe Conditions With the Laser Pistol
Using this laser pistol in the DCTA Metro facility can be beneficial in many ways, but the operator must observe his or her surroundings before deciding to fire. The subway utility pipes often serve as conduit to transport highly flammable gasses. Firing the laser pistol in the presence of a gas leak could cause an undesired explosion and/or severe personal injury.
Section 28.1.1.b.2 - Operating the Laser Pistol Within Proper Specifications
It is required that all DCTA Employees keep the laser pistol pulse energy, length and repetition rate within the specifications diagrammed in the Laser Pistol User's Manual. Failure to do so could result in severe reprimands from the DCTA Regulatory Committee as well as serious personal injury.