Eli5 – what do they use to preserve railroad ties, utility poles etc vs stuff available to common mortals at big box stores?

Question

Most stuff in the stores says 1-2 years decks, 2-4 years vertical. Railroad ties, utility poles etc last decades… what do they use? Is it only available commercially?

In: 1

Answer 1

They use some very toxic materials such as creosote, and as I understand it they are often treated in special pressure chambers that push the preservatives much deeper into the grain of the wood. Not just the top 1cm or so.