Thursday, December 19, 2002

The Jim Crow Presidency...

...of Woodrow Wilson. Stolen from Virginia Postrel and VodkaPundit.

Wonders of dust

I'm not the only reader in the family, but I'm miles ahead of whoever is in second place. Nobody would dare buy me a book as a gift and allegedly I'll read anything.

One day in a bookstore a relative thought she had me. In the sale rack she had found a book so useless even I wouldn't read it - "Wonders of Dust".

It was only a buck, so I bought it. And she hasn't challenged me since.

So why would anyone care about dust? Actually it's a major problem in a lot of areas besides housekeeping. Don't even fantasize about making computer chips where there is dust. Fine particles can enter your lungs and cause problems such as pneumonoultramicroscopicsilicovolcanoconiosis, or even worse when allergens or radioactive substances are involved. Combustible dust can ignite and cause explosions. Dust storms reduce visibility, hurt your eyes and can even render homes uninhabitable. It can cause short-circuits and even fires in electrical appliances and distribution equipment. It can affect the rains and the climate. You can spread diseases with it without "weaponization" - remember the Sin Nombre hantavirus? And it's a way to spread contamination far and wide.

Alright, so it is worthy of study. But what is dust? Just "little bits of stuff"?

That depends on where you are. In the house it's probably flakes of skin from people or pets (dander), dust mites or other small critters, pollen, spores, settled particles of smoke from cigarettes or other combustion, and silica from dirt. So it is highly nonuniform and comes from diverse sources.

Nobody needs to be told that dust can be a nuisance. So how do you keep dust out? You don't - your own skin would fail you even if you could seal and clean the house. But there are mitigation measures for the household.

Of course there are dusters and vacuum cleaners. But these often just redistribute the dust, especially the finer stuff. If you want to get rid of it, there are HEPA (high-efficiency particulate air) filters and vacuum cleaners to trap it for good. HEPAs combined with charcoal filters can even help with cooking odors too.

But HEPA filters are expensive, and in industrial applications where I've used them they were limited to use at relative humidities of 70% or lower. So what else can be done?

There are various other methods yet. They usually take advantage of properties of tiny particles, which do have certain things in common regardless of their origin.

For one, small particles have a very high ratio of cross-section to volume. This means that it has lots of wind resistance relative to its mass. So dust is easily vacuumed, blown away or suspended in air, and it can travel great distances.

Tiny particles also have a high ratio of surface area to volume. Chemical reactions like combustion happen at the surface, at a rate proportional to the amount of surface available. So if there's a lot of surface available, things can happen fast. This is why diesel fuel is atomized in engines, and some otherwise innocuous substances are dangerous when finely divided. Other surface-sensitive phenomena will occur rapidly too - including heat transfer, absorption, adsorption and adhesion.

That high ratio of surface area to volume also means that electrostatic forces from static charges (which are acquired and which build up on surfaces) are very strong relative to the masses of the particles. So it is easy to get fine particles to cling to charged objects. In fact, it's hard to get particles to remain below certain sizes, because they'll start clinging to each other too (assuming the dust is not homogeneous - if it's uniform in composition the particles will all tend to have the same charges and thus will repel one another).

Armed with this knowledge, we know to use electrostatic filters like this one or this active one to provide cleaner, healthier air.

OK, suppose you filter your air - you're not through yet. Your ductwork is probably full of enough nasty crap to keep you in dust for years. So it can be a good idea to have your ductwork cleaned too.

That takes care of getting rid of dust - how do you keep from generating it? Stop smoking. Groom the critters outside. Exhaust your dryer properly. Close the windows. And so on - odds are that much of the time you know when you're making dust.

Admit it, you're impressed - what other blog could have filled up this much space writing about dust?

Monday, December 16, 2002

Megan's Law?

I didn't think I had time to post anything tonight, but then I read this.

I suppose everyone who has seen a doctor show has seen some resuscitation scene where the doctor puts the paddles on the patient's chest and gives them a big shot of electricity to restart the heart. Anyway, lately automated external defibrillators have become inexpensive, simple and sophisticated enough to be practical for use in police cars and private establishments.

What else could such an establishment have handy?

And would they dare? Good ideas have a way of turning into bad laws. Turn our unholy alliance of do-gooders and ambulance chasers loose and the next thing you know waitresses and bartenders will have to have EMT training.