1 March is the one people know about

The annual inventory has a fixed date, so it is the one that gets remembered. The others do not have dates — they start on the day something happens at your site, and they run from there. Nobody writes to tell you one has started.

That is why they get missed. A chemical arrives in June and the three-month clock is over before anyone thinks about Tier II again.

• You brought in a chemical you have not reported before

  The clock starts the day the chemical is first present at your site above its threshold — not the day you notice, and not the following January.

• Your supplier sent a revised safety data sheet

  This one applies to a chemical whose safety data sheet you already sent in. The clock starts when you learn of significant new information on the sheet — a changed hazard classification, a new health effect. Your inventory has not moved at all.

• An extremely hazardous substance crossed its planning quantity

  The clock starts the first day you hold the substance at or above its threshold planning quantity — a number set per substance, often far below 10,000 pounds.

• You have to name a person, not file a form

  Once your site is subject to emergency planning, you must name a facility emergency coordinator and tell the local committee who it is.

• Something changed that affects the emergency plan

  The clock starts on the day of the change — and it is the shortest one here.

The free checker tells you which of these your list has already started, with the date each one is due. That is what the reminders are for.