Time Is Dangerous

"Annorax: When I tell that time has moods, a disposition to be intuited, I'm not speaking metaphorically.

Chakotay: What do you mean?

Annorax: Anger is one of its moods. Anger and the desire for retribution. Vengeance. Time itself has tried to punish me for my arrogance. It has kept me from my wife, denied me my future."

- Star Trek Voyager, (Year of Hell, Part 2)

In many time travel shows, the time machine is generally safe to operate, and the machinery itself is safe.

However, not all time machines are like that. Some could get downright dangerous to use, because trivial mistakes in any time of time machine operation could get time travelers dead. Worse, the world or more could get destroyed by the time machine itself. There can be many reasons on why the time machine itself is dangerous. What if the time machine overlaps matter on its arrival? What if what powers the time machine itself is dangerous, due to various reasons from radioactivity, instability, or just sheer amounts of power necessary? Or, what if some of the time machine's physics requirements are dangerous?

Now, not all time-related dangers are related with time machines. There are also many forms of time dangers, such as those caused by difference in time's flow. For example if there was a bubble of space where time is running 20 times faster, and you stick your hand in it, your hand will get 1/20 as much blood and therefore will start to die! You could lose your hand in a short time.

Temporal Paradox is a sub-trope to this. Compare Time Crash, Hyperspace Is a Scary Place.

Film

 * Time Cop, as explained in the description, requires extremely high speed when they pass through the time travel field. There was one failure that just left two red spots on a heavy steel wall.
 * That said, that's more No OSHA Compliance: After all, they could make the track twice as long to allow safe deceleration on failure...
 * Or make the track a centrifuge, so it'd be trivial to make a second pass at higher acceleration... like one of illegal time travelers did in one of books.
 * In one episode of the short-lived Timecop TV series, the protagonist and his temporary partner (played by Bruce Campbell) find a mothballed time travel lab in the past. They find an early version of the pod still using rocket boosters instead of the so-called "timecop propulsion". When Bruce Campbell asks what happened if the speed wasn't high enough, the protagonist pointed him towards the blackened wall at the end of the track.
 * In Back to The Future, the DeLorean has to be traveling at 88 miles per hour. Which means that unless you know what's going to be in front of you when you arrive in the new timeline, you're going to crash.
 * By the third movie, Doc seems to be acknowledging this. Marty's a little less sure, but both times Doc assures him that the obstacle he's seeing in the present won't be there in the destination time.
 * In Primer excessive time travel causes strange physical problems in the protagonists: mysterious bleeding from their ears and deterioration of their handwriting. Word of God is that this is also a case of Clone Degeneration.
 * In the 2002 film version of The Time Machine, the titular device creates a spherical bubble to protect the occupant. Reach outside, that protection no long applies. The main character hurts his hand when he instinctively grabs at an item he dropped. A Morlock wrestling with him on the machine ends up hanging outside the bubble, aging into dust. Logically, any attempt to reach outside the bubble should have violently scattered their atoms across dozens of years of history, but the Rapid Aging looked cooler, presumably.
 * The directors cut of The Butterfly Effect reveals that Evan suffers minor brain damage every time he majorly changes the past, resulting in severe migraines and nosebleeds as he gets the extra memories (often 20 years worth) burnt onto his existing ones. On the other hand, he's Genre Savvy enough to realise that repeated time travel might ultimately kill him, causing him to intentionally think through what he wants to change before each trip.

Literature

 * In one of Larry Niven's Gil "The ARM" stories, the time compressor invention was used to hide a murder. First, a witness was murdered in an impossible way - his head burnt to ash. Then another witness lost her arm poking the compressor, as she stuck her arm into an area where time moved faster - and deprived it of blood for several minutes. In the final arrest, the murderer was stuck inside the bubble and the cop was outside holding on to him by his legs. Unfortunately, the compression of time affected the killer in such a way that he died by thirst. Yes, the cop literally held the killer till he died of thirst.
 * Oh and how did this murderer kill? That was the reason the cop had to hold on -- the killer was trying to get to that.
 * The effects of double time compression (One inside another) were discussed, and one of effects is that light speed inside the time compression sphere would be just a few feet per second. It means if a punch was thrown, the arm would get shorter!
 * In Time Ships, the time traveling jeep was blown to pieces by intersection with a reverse growing tree while they were traveling backwards with expiring fuel. Lucky, the time travelers survived.
 * One of Michael Moorcock's Dancers at the End of Time short stories has a time traveller trying to warn her era about the future, only to find that time itself won't let her. The harder she tries the more her time machine overheats, but she refuses to give up and dies in agony.
 * In the novel Timeline, travel is accomplished by copying the information required to rebuild a perfect copy (at the atomic level) of the traveler and beaming this information into the past. Errors in copying are possible (in fact, inevitable if the machine isn't properly shielded) leading to Clone Degeneration.
 * The beginning of the film version, the dead scientist's body scan revealed that part of his body appear to be slightly shifted from their normal place.
 * In the short-short story "The Man from When" by Danny Plachta a time-traveller arrives from the future and states that his departure caused such an expenditure of energy that it completely wiped out the Earth of his time. He then reveals that
 * In Kevin O'Donnell's story "Gift of Prometheus" a malfunctioning time bracelet freezes its wearer outside of time and space with a bullet in his gut, unable to do anything but suffer and wonder if it will last forever.

Live Action TV

 * In a Star Trek the Next Generation episode, "Timescape", Picard is injured when he sticks his hand across the edge of a "time bubble", which causes his fingernails to age faster than his arm. Later, he experiences symptoms of "temporal narcosis" due to a malfunction of the equipment protecting him from being frozen in time.
 * Ironically, its mentioned that taking the "armband" off would merely freeze someone in that timeframe with no ill-effects from the rapid transition from one to the other. Time is funny like that.
 * A Star Trek Voyager episode "Shattered" has Chakotay end up in a temporal anomaly that results in various parts of his body having different ages. The Doctor manages to stabilize him. Apparently, they covered this at the Starfleet Medical Academy.
 * Another episode "Blink of an Eye" has an astronaut from a planet were time operates in a faster rate than the regular universe, ends up dying during the transition to the timeframe on Voyager, while the other one barely survives.
 * In one Outer Limits episode, the result of Ripple-Effect-Proof Memory is that an entirely new lifetime's worth of memories gets added onto the existing one, which could result in brain damage.
 * Another episode had a time traveller end up a few days in the future to see his wife dying from a gunshot wound. He goes back and tries to prevent it. However, the side effect of the trip is physical and mental degradation. By the end, his wife has had enough and decides to leave him. In a deranged state, he ends up shooting her. Seems to be a case of You Have Already Changed The Past, doesn't it? Then the episode does a 180 on this idea and has the guy go back to the night he first met his wife and shoot his younger self, himself turning to dust. Of course, the worst part is that she was planning on killing herself that day.
 * Seven Days. There are so many things wrong with the Sphere. First of all, while it's very accurate in time travel, landing it where you want to be requires precise piloting. Second, Our Time Travel Is really painful. Third, well, go to the page and check out the list of Phlebotinum Breakdowns the machine suffered. That's probably not even the full list!
 * Sanctuary: A time bubble allows people to enter, but violently destroys anything attempting to leave. Time inside the bubble runs six years to each day outside, resulting in three-year periods of no sunlight. Naturally, this is not good for a self-contained ecosystem. Furthermore, if the bubble had expanded too far, the time differential between the different parts of the Earth would have destroyed the planet.
 * Sapphire and Steel: Time is outside the (metaphorical) safe corridor in which human life and history exist, and it is constantly trying to exploit weak spots in the corridor walls and break in. This, when it happens, is not a good thing. Time is the enemy.

Newspaper Comics
"Hobbes: Why do we have to wear goggles?
 * In this Calvin and Hobbes, the dangers of using a cardboard time machine are discussed.

Calvin: Geez, do you think traveling years into the future is like driving down the street?! We've got to contend with vortexes and light speeds! Anything could go wrong! Of course we have to wear goggles!

Hobbes: Gosh, I think my goggles are in the bedroom. If I'm not back in a couple minutes, you can go without me."

Video Games

 * Achron: You can Chronoport your units back in time. It's like teleporting, but for time instead of space. You just need to make sure the arrival point isn't occupied by anything. Like, say, your unit's past self.

Web Comics

 * This Mindmistress story explores some dangers of time flow differences. Among other dangers, it's very unwise to hit anything hard while sped up.
 * This Real Life Comics strip touches this with discussion after time bubble were used to rapidly age mead 6 months.

Web Original

 * Cracked.com has a list of reasons why time travel sucks.

Western Animation

 * In the Batman the Animated Series episode "Time Out of Joint", Clock King uses a time-altering device to trap Batman and Robin in a "bubble" of slowed time, where seconds for them pass as hours on the outside. Batman points out that objects "outside" the bubble are moving relatively at tens of thousands of miles an hour while they are comparatively "standing still". Meaning there will be an enormous (think asteroid impact or nuclear weapon) explosion if anything collides with them in their "frozen" state. Fortunately Batman defuses the trap before it can happen.