# Acid as a Threat
A pivotal element of the Nadir "experience" is the presence of a looming threat, and acid is the current selection and primary candidate. Below, I hope to break down the reasons I believe a custom acid is the best source of looming threat for Nadir, and the ways in which it can be tuned to a satisfactory level of danger that creates this threat without being insurmountable.

## Advantages

* **Multiple avenues for tuning.** The level of damage the acid deals, the ability of equipment to mitigate and withstand that damage, and the ability of the station to resist breaches or contain their spread can all be adjusted extensively.
* **More interesting mitigation.** With a threat like radiation storms, you'd just get rad suits or interdictors, making for flat gameplay, and other threatsh like hostile critters essentially consist of "don't go outside", unless they invade (which would likely be frustrating); fluids can be dealt with by shielding, drains, fluid tanks, or even buckets if you're desperate, and by integrating equipment degradation from acid, gear can offer total protection but with a different level of sustained protection.
* **Strong narrative presence.** The planet on which Nadir is sited is highly inhospitable, and acid provides a lot of ludonarrative cohesion in this regard; the design and systems are tailored around staying operational in this alien and inhospitable environment, one that doesn't want you dead out of malice, but simply because this is not somewhere people were meant to be.

## Potential Hindrances

* **Free acid = crime time.** While the acid is considerably reduced in strength versus something like fluorosulfuric, it's still a free supply that people can drag people through or scoop up and splash onto things. The acid should likely be tuned weak enough that this won't be too catastrophic (it can be dialed down a decent bit and still be enough of a threat to consider), and with regards to the dragging in particular, a "fluid contact loop" was proposed.
* **Reagent shenanigans.** Since the acid comes out in a fluid pool, people can do things to that fluid pool; inability of the acid to be vaporized (if possible) will likely be an important step here, but more consideration is probably warranted. PR 9904 may also be relevant here.
* **Breaches are currently kind of easy.** ex_act at maximum magnitude will **always** breach floors in its current state, no matter if they're reinforced; ideally, it would take a little more effort to breach on Nadir, but I don't know how this might be done. This is mitigated somewhat by the counter-spread measures.

## Station-Based Protection

Very few countermeasures of this sort were present for Nadir's first officially-supported test, making it likely that acid would spread far and wide from even the tiniest of breaches. This should change, and has.

### Extensive Door-Linked Forcefields

This is the solution I've currently implemented in the wake of the test, as a simple countermeasure. It strikes me as a protective element that could remain, with the following advantages in mind.

* Straightforward in operation; doesn't rely on breach sensors or anything networked, which could be destroyed in explosions and result in a failure to activate containment.
* Friendly to Classic servers; people barging through breached but powered areas won't cause the acid to propagate further, just melt themselves if not properly protected.
* Makes loss of power considerably more meaningful; with power deactivated, door shields will fail to activate on doors opening.

It's been suggested that this makes breach confinement "too easy"; I'm of the opinion that breaches which actively spread danger should have appropriately strong countermeasures, but this point was raised so I'm sharing it here.

## Personal Protection

An important foreword here is that my implementation of chemprot damage mitigation for acid floods **was not operating as intended** during the live test due to poor selection of the calculation step where chemprot was applied. This has been changed, and chemprot now (more or less) mitigates the percent of acid damage you see in your character stats.

The current state of personal protection is as follows.

* Primary, full protection is available from chemical protection suits, which fully withstand the acid but offer limited protection from cold. In addition to EVA, several are available in acid response lockers dispersed around the station.
* Limited mitigation is available from assembling chemprot gear, prominently including bio-suits and spacesuits / derivatives, including the emergency suit. Black shoes and a quartermaster's jumpsuit in combination with an emergency suit will give you 60% chemprot, elevated to 75% with the addition of appropriate gloves; this gives you enough mitigation to move through floods without taking critical damage.
* Gear will not decay whatsoever in contact with acid.

This state has several inadequacies; partial protection feels awkward and is effectively useless in practice if you need to conduct repair work on damaged areas, while those in possession of full chemsuits are effectively immune to the acid but don't get enough thermal protection to operate outside without getting excessively cold.

What follows is a description of (more or less) how I'd like the personal protection situation to look once everything is sorted out.

* Primary protection is available from immersion suits, which protect from both the acid and cold and are available in departmental variants. Appropriate variants can be assembled at most manufacturers and are included in acid response lockers as well as EVA, and they are able to accept armor. They degrade slowly in contact with acid, taking a long time to fail.
* Secondary protection is available from any pressure-sealed suit set, such as emergency suits. These will degrade faster in contact with acid, but **still offer you full protection** until their durability runs out, and last a solid few minutes. Emergency suits are distributed to all crewmembers by default (this is already added at time of document writing).
* Tertiary protection is provided by your chemprot stat, partially mitigating the damage you take from acid.
* Equipment decay is represented by a visual indicator of some sort; my current concept for this is a small "pip" that serves as a rough indicator of gear health, similar to the player health indicator.
* If the equipment hasn't been decaying recently, it can be repaired with a mending tool. These tools accept mending thread cartridges which can be fabricated from cloth and metal, and restore equipment durability over time in an auto-mender-esque fashion. They are included in acid response lockers and other locations where EVA equipment is stored, with at least one replacement cartridge alongside each; the tools themselves can also be fabricated.

I definitely need assistance for some of this. I've already enlisted help on the immersion suit art, and codewise I'm curious for thoughts on the decay system; I made a previous attempt in PR 8145 / branch "meltygaming", but I'm not sure that the approach I took was correct.

## Footnotes

I've been tinkering a bit with other acid properties, in addition to the resequencing of the chemprot check. The viscosity was increased slightly (making it a little slower to spread) and the damage formula was adjusted a bit; there **will** need to be further changes if global chemprot (currenly PR 9904) gets in, of course.

If you have any concerns or qualms about the acid that I haven't addressed, please feel free to message me at any time; messaging over Discord is the most likely spot to get a response, as it's where I check most frequently.