# How hot does a shield made of fire need to be? [duplicate]

Consider a pyromancer that uses weapons and defense/armor made entirely of fire. I realize that one issue with this concept is the compressibility and thinness of plasmas. An object may easily pass through a flame. while said object is burned, it is not stopped.

Is it possible to make an effective barrier against physical weapons using fire? If so, is there a temperature, thickness, or type of fire/plasma that would be able to do any or all of the following when used as a "shield":

1. Stop or deflect metal objects
2. Incinerate wooden arrows before completely passing through
3. Melt alloy and light metals in a "reasonable" amount of time - several seconds

I appreciate greatly any answer that also touches on the localized air pressure differences generated by high-heat flames, and also the magnetic effects of controlled, compressible plasmas (specifically with regards to ferric metals)

Bear in mind, the pyromancer in question will be immune to the effects of the heat, and thus his/her well-being is not an issue. Similarly, there are counter-measures for side-effects of great heat such as blinding brightness. Assume the construct will be held in shape during the interactions with other objects.

• Simply melting the metal will not stop it. Even completely vaporize it wouldn't stop it. The kinetic energy of the swing will mean what ever is being swung at you will keep moving towards you and that energy will still hit you in some way. This is true for real shields as well. So anyone physically much stronger than you will knock you over with the force of the swing if you attempt to block it. Aug 9, 2017 at 17:57
• In my answer to the pyrokinesis question sphennings linked I tried to do some math to estimate volume change with temperature change and what sort of windspeed that would make. The specifics had to do with stopping bullets. Aug 9, 2017 at 18:21

It would not be effective.

If you had a fire shield hot enough to instantly melt a sword as it was swung at you. It would be hot enough to destroy the ground you walked upon. You would be standing in a pool of molten sand. You would not be able to do this near anyone not protected from the extreme heat, or near any structure or building.

Even if you do melt an object it will still have the same amount of kinetic energy and will still hit you with the same force.

A bullet of molten lead will actually transfer more of that energy to you. Increasing the lethality.

• Yeah that melting the earth you walk on is a problem unless you just umbrella it under "wielder not affected".
– Ash
Aug 9, 2017 at 18:19
• I want to mention that it looks really weird that you marked the question as a duplicate and thereby said it already has an exact answer somewhere else while writing your own answer on this question, which looks like you thought there is more to say to this specific question. See for example the Rules of Peer moderation rule 8 "Don't answer a question that you voted to close." Just for my interest: What made you VTC the question and answer it at the same time? Aug 10, 2017 at 8:20
• @secespitus I didn't discover the duplicate until after I had a answered the question. Thank you for pointing this out to me. Do you think I should delete my answer? Aug 10, 2017 at 11:45
• I don't think it's necessary because you found the duplicate after you answered the question. The other way around would be a bad example for new users. As there is currently no edit history it's not possible to see when you VTCed and when you answered, that's why there was this confusion and why I asked about it. It just looks weird when taking a close look. Aug 10, 2017 at 12:02
• This question took too long to close. Aug 10, 2017 at 12:05

It's basically a question of either particle density or horrific amounts of heat, you can have a shield that has the physical properties of steel that will deflect or stop everything that hits it. And/or you can have it be really ridiculously hot you'll want it to be at least 500 Degrees Celsius to autoignite wood to actually incinerate an arrow I'd double that at least, 1500 Celsius will also burn steel weapons the Iron oxide powder in reasonable time (that's fresh lava type temperatures you may end up wading through the glass that used to be the fields around you). Hope that helps.

It would work, to a degree. (Nice pun, eh?) People are right that the momentum (MV) and kinetic energy (KE) of whatever is being shot at you or swung at you would be unchanged. BUT! It would be spread out over a bigger area, because the front of the hitting object would explode as the object entered the heat shield. This would impart sideways and backward MV and KE to the rest of the object. The total MV and KE would still be unchanged, but it would be spread over a sphere. If the heat shield were far enough from the pyromancer, some of the blast would miss him entirely, and the rest would hit his body evenly. For an arrow, this would protect him. For a boulder thrown by a giant, probably not.

However, if the pyromancer turned up the temperature too high, then the shield would turn the weapon/missile into a hot gas, which would expand spherically with a large explosive force. Even a pebble tossed into his shield would send him flying. And deafen him. Not good.

• On the other hand, the melted fragments would be on fire when they hit you. Aug 9, 2017 at 19:34
• @Draco18s fire shouldn't be a problem for a pyromancer tho Aug 9, 2017 at 19:43
• @A.C.A.C. That depends on whether or not they can control "not quite molten metal" the way they can control "plasmatic fire." Aug 9, 2017 at 20:30