[manifestsilence]

My guess from having formerly been married to a chemist is that machine-based chemistry is one of the most difficult areas of science. Chemistry is still equal parts art and science in that the techniques that will give accurate scientific results depend greatly on the types of things being measured for. For detecting a particular substance, there may or may not be a cheap or viable detecting device that could be built, depending on whether that thing is normally detected by chromatography, reaction with something else, spectroscopy, etc. For example, carbon monoxide detectors are great and cheap. But I think it's probably just really case by case. Chemistry is just super hard to generalize or systematize. I used to ask her why they don't have Star Trek tricorder type devices yet that can universally analyze substances, and that was more or less her answer.

Edit: for the difficulty of machine chemistry, see also the Theranos debacle.

[guitarbill]

Carbon monoxide might be easier because it's one specific molecule, and the concentration has to be fairly high (comparatively) to be life-threatening. The paper mentions VOC (volatile organic compounds) which are probably harder to quantify. Detectors aren't always great either. I've worked in labs that didn't use helium detectors, because - at the time maybe - they weren't super reliable, but having them usually meant people would rely on the detectors instead of paying attention to the symptoms of a helium leak.

Smell/organic chemistry is weird, too. Some molecules have similar smells, despite being sometimes quite different. Many molecules have quite different smells, despite being not that different [0], edit: the esters table maybe shows that better, [1].

[0] https://jameskennedymonash.wordpress.com/2014/01/04/table-of...

[1] https://jameskennedymonash.wordpress.com/2013/12/16/infograp...

[manifestsilence]

Oh yeah, I'd forgotten how weird smell in particular was. I seem to remember at the time that there were three competing theories for how smells are even perceived or what gives a substance a particular kind of smell, and each only explained a subset of smells.

For the helium leak, is one symptom a high squeaky voice, or is that at already really dangerous concentrations?

[guitarbill]

From what I remember, dizziness, headache, inability to concentrate, etc. You'd notice a big/quick release as the liquid helium boils of quite easily. A slow leak is more dangerous, in which case you might even get used to the higher pitch without noticing.

[fwip]

One symptom of a helium leak is that your iPhone might stop working: https://motherboard.vice.com/en_us/article/gye4aw/why-a-heli...

This happened also to the coworkers of a friend of mi e - occasionally everyone's iPhone in their office would stop working. Android phones still worked fine. Later (after this article was published) they found out there was an MRI machine downstairs.

[hinkley]

Isn't carbon monoxide also a ridiculously simple chemical? Detecting complex molecules has to be a lot more complicated, doesn't it?

Also noses self repair. You can foul them with another scent for a while but eventually the receptors will recover.