Re-entry Interval (REI)

The REI is a label instruction with the force of regulation behind it, not a courtesy estimate. The regulatory definition sits in the agricultural Worker Protection Standard, which defines the interval as “the time after the end of a pesticide application during which entry into the treated area is restricted”; structural and residential products are not covered by that standard, and their labels carry their own re-entry or ventilation statements instead. Either way the principle is the same: the clock starts when the application ends, it applies to the treated area, and it is the reason a job is not finished when the sprayer is empty: someone still has to know when the space can be occupied again. The re-entry interval timer works out that time and prints it as a field notice, so the customer has it in writing.

Because the interval comes from the product, the first question on any job is which label applies, and on a restricted use pesticide that question arrives with a second one about who is allowed to apply it at all. The EPA points applicators to the labeling itself, noting that some products carry one REI for all uses while others vary it by crop, application method, or the task performed afterward, and that when two products with different intervals go down together the longer one is followed. Tank mixes are where crews get this wrong: the mix inherits the strictest clock in it. Swapping to a different-strength product with the same active ingredient brings its own REI, whatever equivalent rate the product swap calculator returns. Space treatments raise the same clock from the equipment side, where the ULV fogger calibration calculator turns a measured flow rate, ground speed and swath width into the output an area is really receiving.

Documentation is the other half. The application record, the posted notice, and the clear-at time you gave the customer should agree, which is what the pesticide application log worksheet is for. Licensing rules that sit behind all of this vary by state and are collected in the pesticide applicator license guide; the dilution and rate side lives on the pesticide dosing guide and the rest of the trade’s math on the pest control hub.

Operationally a re-entry restriction is a scheduling constraint as much as a safety one. On structural accounts the figure comes from the product label rather than from the WPS, but it binds the calendar the same way: a long interval on a commercial kitchen or a school corridor decides which night the work happens, how the work order is written, and whether the crew can stack another stop after it.