If you've ever seen movies about World War I, you know thatthe soldiers in the trenches often wore bulbous gas masks that made them look like human insects.
如果你看过关于一战的电影的话，你肯定知道冲在一线的士兵们通常会配戴着球茎形状的防毒面罩，看起来很像人形昆虫。
The masks were necessary to protect them from chemical weapons such as chlorine gas, a noxious substance that could almost instantly suffocate unprotected victims.
这种面具可以保护士兵不被化学武器攻击，如氯气-一种可以快速使人窒息的有毒气体。
If chlorine is so dangerous, why the do we dump it in swimming pools?
如果氯算危险物质的话，那么为什么我们要把它倒进游泳池里呢？
As you probably already know, chlorine is used to disinfect swimming pools.
你可能已经知道，氯可以用于消毒游泳池。
It also gives mostpools their distinctive odor.
同时，大多数加氯的游泳池也会有一种独特的味道。
Chlorine comes in pellet, liquid, and gas forms, and when it reacts withpool water it immediately breaks down into different chemicals, including hypochlorous acid and hypochlorite ion.
氯可以以固、液、气三种形式存在。氯遇到水会立刻分解成不同的化学物质，如：次氯酸和次氯酸盐离子。
Both chemicals attack micro organisms in the water by breaking through their cellwalls and scrambling the inner workings of the cells, rendering them harmless.
这两种化学物质都可以通过破坏水中微生物的细胞壁、扰乱细胞内部正常运转而使微生物变的无害。
So why don't these killer chemicals destroy human cells as well?
那这些致命的化学物质不会破坏人体细胞呢？
They would, if not for the verysmall amounts of chlorine needed to cleanse the typical pool.
如果用于清理泳池的氯使用量过大的话是会对人体造成伤害的。
For example, the concentration of chlorine used to sanitize an Olympic-size pool is three parts per million, meaning that for everythree molecules of chlorine there are one million water molecules.
比如，用于奥运会的泳池消毒的氯浓度是3比100万，也就是说每一百万个水分子里有三个氯分子。
Such low concentrations may cause slight irritation to the eyes and skin, but there's not enough chlorine to cause any real harm to swimmers.
这样的低浓度可能只会对眼睛和皮肤产生轻微刺激，但对游泳的人来说不会产生真正的伤害。
Chlorine is not the only chemical used to keep pools clean—bromine and ozone are becoming increasingly popular in pool maintenance facilities.
氯不是唯一能够保持泳池清洁的化学物质-溴和臭氧在泳池的日常维护中也越加频繁。
But chlorine is still the pool cleaner's mainstay.
但泳池清洁人员主要还是用氯来消毒。
