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Chemical and Biological Warfare

HAZMAT Suits and Endurance

Many people here have been in the military and understand the destructive effect HAZMAT suits have on endurance and functionality. However it's difficult to represent anecdotal information in a game environment so I thought I'd post the two primary systems that cause that degradation of ability.

First and probably the most notable is heat build up.
Not being able to escape the heat your body generates is an incredible and unpleasant experience but the effects are not only overheating but the actual composition of your muscles change. They become less elastic and lose the ability to flex. This is not a linear progression but rather a bell curve as the effects rapidly degrade after a steady decline. I can't over-emphasis how dangerous this is. Not only can the victim's organs shut down and brain damage occur but in extreme cases the muscles can actually stop being elastic strands and become just masses of jelly-like tissue. In a twilight 2000 environment there's probably no possible recovery from this and a lingering death is almost certain.

The other one is exhalation of carbon dioxide. Both these two are linked. Carbon dioxide build up occurs because HAZMAT filters cannot pass nearly enough air through them to both give the lungs the required oxygen and expel enough carbon dioxide. Physical exertion builds up lactic acid in the bloodstream that is broken down in the organs and then expelled as carbon dioxide. If this can't be done at the correct rate a logjam occurs in the body and the lactic acid is not broken down. The upshot of this is the body fatigues very quickly.

So there's three primary systems working here; heat build up, oxygen intake restriction and carbon dioxide expulsion restriction.

The effects tend to snowball and also create feed-back loops which increases the snowball effect.

In game terms what happens is the character is in the three work states given in the rules; rest, light work and hard work. The saves are harder for each work state as the work gets harder.

An important thing about this mechanism is it's very unlikely the PC will notice the effect happening before other, watchful PCs do due to the disruption of brain activity. This isn't like ordinary heat-stroke, it's much faster occurring and more damaging, especially as the usual methods of relieving heat stroke cannot be maintained in a HAZMAT environment. So the GM should apply Observation checks for team mates to see the effects occurring and the victim has a much higher save on the roll.
Contaminated Environments in the Game

I'm a big believer in the MOPP suit. I think at least once in each campaign a hazardous environment should be encountered to bring home that this was a Nuclear, Chemical and Biological War. This is not a summer Sunday afternoon in the woods.
As it's a bit unfair to inflict this sort of nightmare on unprepared PCs it's best to use the universal "I Show, You Do" approach where the PCs can see someone else go down with this, how it occurs and what the effects are.

On a game note to varying effects even just gas masks do this with less but still some heat build up.
Now, having the OPFOR dump some VX on your PCs as they drive along is probably going to get you some hard stares from across the table. Harsh campaigns might have this, my campaigns are very harsh and I wouldn't, but normally it's best to give the PCs both a bit of reaction/preparation time and access to at least normal protective gear. This means you'll need a significant carrot and/or stick to send them into the environment about which the players probably have few illusions about.

There are two main differences in the situation apart from environmental factors; Attacks and Contaminations.

An attack means the risk is acute. The level of contaminants are high and none have had time to degrade. These are extremely hazardous environments where a failure of the containment systems probably means heavy exposure. Obviously these are rare. To be frank the players are nearly never important enough for the OPFOR to expend precious contaminants purposefully on them, however there are many gas mines used by both sides that might create this situation. Generally I tend to use those as events that happen to other people (they are great for blocking off avenues of exploration) but as it's your game I leave that to you.

Contamination is a far more common situation and this gives the PCs several options an attack does not, not the least of being simply to avoid the contamination. In this case a failure of the protection does not necessarily mean exposure depending on the nature of the contamination. Some contamination are so persistent they can be be considered permanent Attacks. One of the biggest problems in a contamination environment is that the individual goes through cycles of hyper-vigilance, awareness and negligence. Once again other PCs can monitor the player. As a side note hyper-vigilance is fatiguing. This is not a good situation for the player. If the player becomes negligent then the normal risks of an exposure increases dramatically. As this has such severe repercussions I'd suggest the GM let this be based on player attitude rather than arbitrary dice rolls and leave those to NPCs. The Leadership skill can buff rolls here.

There is an enormous amount of literature on the effects of contamination and decontamination which I won't go into here. The GM should take into account the amount of weathering and degradation of the contaminant. Weathering degrades exposed surfaces and leaves unexposed areas less effected. This makes simple things such as going over a fence hazardous because the bottoms of the railings may still be heavily contaminated. Also note that some agents rapidly break down, especially some biological agents, and can cause far less damage. If you really want to give your PCs a heart attack have them become inadvertently exposed to a serious agent that has degraded to the point here it is about the level of an irritant.