https://whitelungdisease.blogspot.com/

Why White Lung Disease? It may help to point out that I served as a teacher before dry-erase boards replaced chalk boards. For that matter, I still remember mimeograph machines, overhead projectors and six classes a day.

Here’s a useful analogy –
coal miners: coal:: teachers: chalk.

Coal miners had the advantage of bringing canaries into the deepest recesses of their workplace to detect the presence of poisonous gases. Plus, canaries can at least learn the rudiments of language.