Note that a new OSHA requirement has been released and API is not currently aligned. The OSHA release is literally month(s) old. API will address the issue in it's next addendum but for now you should refer to the new OSHA standard.
IFRs- if you go to the OSHA.gov page and look under "Rules and regulations", that is updated to the new rules. The latest CFRs (2016) are still the old rules. If you find the new rules in the Federal Register pdf, they're easier to read- you have to download a 900 page volume, and the new rules are the last 50 pages or so.
Might have an old version of API-650, but seems straight forward that any API-650 tank with platform/walkway/stairway shall have handrail, midrail and toeboard
Table 5-17 Requirements for Platforms & Walkways
"The height of the top railing above the floor shall be 42" (This handrail height is required by OSHA specifications)"
This is in agreement with OSHA 1910 for handrail height
JGard- one issue is not whether to have handrail, but where to have it. Typical tank handrails will be a few feet either side of the stair platform or ladder, then nothing beyond that, but that arrangement is hard to justify per the older OSHA rules.
As for 42" tall guardrailing, we as a company go 12' each side of the top platform...trying to keep all our nozzles within 6' of the platform. We go all the way around with guardrails if the tank is less than 15' in diameter.
Handrailing is another subject that will soon be a headache. We've typically taken advantage of guardrailing on the stairs for handrail use but IBC code seems to call out for a handrail at 34 to 38" and it can't be angle...this is going to require a separate pipe handrail below the 42" guardrail on tank stairs eventually and also either eat into the available space or require wider stairs.
