Let’s do it.
Ring of fire
MacGyver uses a fire hose to spray gasoline on the ground and then Jack ignites it with a bullet. It looks cool, but there are two problems. One small problem—bullets don’t make sparks (usually)—http://www.cracked.com/article_19781_6-stupid-gun-myths-everyone-believes-thanks-to-movies.html.
Oh, also gasoline doesn’t always burn that well.
OK, but gasoline CAN burn and bullets CAN make sparks—so this isn’t completely crazy.
Fixing an inhaler
MacGyver uses part of a plastic force to fix the part that pushes the release valve of a broken inhaler. This is exactly the kind of thing MacGyver would do.
Battery hydrogen bomb
OK, this is mostly real—but very awesome. Here’s how it works. If you put an electric current through some water, you can break the water into hydrogen and oxygen. In order to do this, you need the water to be able to conduct electricity. NEWS FLASH: pure water doesn’t do this. If you add some salt, water conducts just fine.
Now with the current going through the water, you get tiny bubbles. Bubbles on one electrode (I can’t remember which) are bubbles of hydrogen gas. The other set of bubbles on the other electrode are oxygen.
You can seriously do this on your own. It’s really not hard.
But how would you make an explosion? You can let the hydrogen and oxygen gas mix together—nothing will really happen until you get a spark to star the reaction between the two gases at which point BOOM.
So, in the case of MacGyver he wants to let the hydrogen gas collect at the ceiling. Yes, the hydrogen gas would rise but it’s also difficult to contain. Any tiny crack and it’s gone—but still, it’s a good idea.
What about the ignition? A spark will do. Yes, you can indeed get a spark from a fluorescent light. Especially from the ballast since it makes a high voltage.
Oh, one more comment. What about the 2 psi pressure difference? Is that possible? Probably. Would it knock the door off? I think so—especially if the pressure change is quick. Would it be bad for humans? Could be.
Morse code with the tail lights?
Final breakout part 1: making liquid nitrogen
OK, this is a stretch. MacGyver uses a carbon dioxide fire extinguisher and some alcohol to make liquid nitrogen. It doesn’t say liquid nitrogen, but that’s what it is (from the air). Let me just show this video:
See. It’s possible. It’s not easy, it’s possible. What about the dry ice? Well, that’s another stretch. Expanding carbon dioxide from a compressed tank CAN INDEED make dry ice. In fact, that’s how we do it in chemistry sometimes.
Final breakout part 2: breaking steel
MacGyver takes the liquid nitrogen and puts it on some steel bars. The get super cold and breakable. The first problem: you would need a lot of liquid nitrogen to cool off the metal. But OK. The second problem—there really isn’t another problem. If you get it cold enough, I think it would work.