Here's the instructions for the Mark IV Thermonuclear Device seen Half-Life: Opposing Force that destroys Black Mesa. You have to have a really long stick to press the B button from 55 kilometers away. MANUAL INSTRUCTIONS FOR A: MARK IV THERMONUCLEAR DEVICE This device carries a GRADE C plutonium control detonator. With this device an approximate safe distance of 55 kilometers is recommended. STEP1: Indispose the gravatronic rev limiter to 11. STEP2: Rotate red knob to the on position. STEP3: Press button labeled B.