Where it is
Last element of the ISPM 15 mark.
What it proves
That the wood reached at least 60 °C for 1 continuous minute throughout its profile, surface included, using microwaves or radio waves.
In detail
DH was added to ISPM 15 when Annex 1 was revised in 2013 and kept in the 2018 revision. It is a heat treatment, but with its own code because the parameters differ from a kiln: 60 °C for one minute instead of 56 °C for thirty. For wood thicker than 5 cm treated at 2.45 GHz, the standard calls for bidirectional application or multiple waveguides so heating is even.
Canada's directive D-98-08 lists dielectric heating among its approved treatments, and US rules accept marks approved under the ISPMs, though the example in 7 CFR 319.40-3 names only HT and MB. In practice DH is rare on euro pallets. EPAL's own pages describe heat treatment in a kiln, so most EPAL pallets you see will be marked HT.
If you find DH on a pallet with EPAL brands, it is not a fault in itself; decode the rest of the stamp as usual.
Common misreadings
- DH is not 'double heat treated'. It names the dielectric method.