Anyone buy placards?

The thing is, when you say "if it meets the threshold", you are referring to a requirement "otherwise provided" from the general rule, which initially says any amount has to be placarded, yet it is otherwise provided that there's a threshold where it wouldn't here.

Then to say that even though affixing placards is not stated as a shipper requirement in this situation, you are relying on a premise that the general rule cannot be "otherwise provided" for, except in fact, it is otherwise provided that only the carrier has to affix them there.

The general rule says upfront "unless otherwise provided", because it doesn't apply to every situation, and this is one of them (like where "any" amount of hazmat may not have to be placarded). The general rule also does not say when it must be placarded, or by whom, because that's what the other rules are for. You might assume that 'when' would correspond to any amount being in a trailer, but then not any amount has to be placarded at times, just like another rule states that the shipper must at least provide those at the time in which it is up to the carrier to affix them, if not sooner. If the trailer had to have placards affixed by the shipper, prior to the carrier doing so, it would surely say so. We're talking about highway transport here, and going beyond that it looks like we're talking about OSHA standards, which also do not say that.

 

The section symbol § is not a subchapter, and .504 is a general requirement section referring to other sections in the subchapter, which would be 172. If not, why would general requirements otherwise provide for themselves in the same section? That would be what another section was for, I'd say (such as §172.506). Makes for tedious reading either way...

That, and the hazardous materials guidebook seems to reflect such a format, where it doesn't refer to placarding by shipper as a general rule (based on that section).

Yeah, there it is: Title 49 → Subtitle B → Chapter I → Subchapter C → Part 172 → Subpart F → §172.504

Wild guess on my "part" there... close enough. So the section is .504 of part 172 of subchapter c (and subpart f includes sections 504, 506, etc).

Well, as orders of operation go (dialectically), further reading for this might be found in other parts of the subchapter too... kind of an odd format (back and forth), or not all that unusual in this forum type o' context, section 8 (?), page eight, whatever. The general section did include some other provisions too (like the weight threshold), so unless "subchapter" was a typo, the rest could be stated anywhere in the hazardous materials regulations.

Again though, I think the guidebook exists so we can read what is pertinent from the CFRs in order. Looks like there are also several OSHA guidebooks out there... wonder which one that's in. Ah, there it is: OSHA General Industry Regulations Book, 29 CFR 1910 ("Make compliance with dense government safety regulations simple..."). Who knew?

As far as the hazmat pocketbook goes, it says large freight containers (640 cubic feet or more) must be placarded by the shipper, although the CFRs differentiate between a freight container and a transport vehicle (which a 53' one is said to be 3816 cubic feet), so that's an example of a separate and more strict part/section in which "placarding" would be on them (not the train engineer, or whomever transports the freight container). I'm sure it mentions bulk transport too, and just depends on what a particular section says in the CFR (which includes the OSHA stuff, unlike my pocketbooks—same goes for the FMCSA one that also sources 49 CFR and leaves out 29 CFR, in the chapter on hazmat).

Slightly different format in 29 CFR too:
Title 29 → Subtitle B → Chapter XVII → Part 1910 → Subpart Z → §1910.1201

Goes from chapter to part, skipping subchapter. Then the subparts span a number of sections of the part. I'm gonna go back to studying lug nuts... and say a chapter is like a tractor, which can have a trailer (subchapter), and each have parts in common (like wheels), which consist of sections (tires, rims), that may be separated into subparts (nuts).