ISPM 15 Heat Treatment

[AdamT]

Your question #1 on the efficacy of ISPM15 is a good one. As your example shows, wood remains susceptible to fungi (and insects) after heat treatment. I believe (can't speak for them) that the primary intent of ISPM15 is to reduce the risk of spreading insects that may exist in green lumber - the heat treatment will do that. If the intention was protect the wood from harboring wood-infesting organisms over its service life, then I think it doesn't do much if anything. I like the idea of preservative-treating pallets to achieve long-term protection - but I understand that some customers are adamant about no chemicals. Plus it would be an added cost.

 

[HencoV]

We recently did an installation on a kiln to do heat treatment of pallets to comply with ISPM15 heat treatment regulations. The client runs a small pine sawmill and dips all timber in anti fungal dip. He then manufactures the pallets, followed by the Heat treatment of 56 Deg C core temp on the thick bearer part of the pallet for 30 minutes. DB temp goes up to 80 Deg C.  After this the kiln goes over into a drying cycle. (more to prevent the hot water boiler from boiling over than actual drying!, though it does get rid of free surface water)

Despite all the above the pallets started growing fungus at a client's storage facility (in a shed) during a particularly humid period, less than a week after manufacturing and treatment.

During HT the humidity in the kiln goes very high and water start accumulating on the timber surface and on the kiln floor. We suspect that this "washed" off the anti fungal dip, or the 80 Deg C temp may have de-activated the active ingredient of the anti fungal dip. Further the MC of the pallets were not reduced significantly enough to prevent fungal growth to re-appear under perfect fungal growth conditions in a shed that was probably saturated with spores anyway.

This leads to 2 questions:

How effective is ISPM15? Is this not just to "stop the buck" at the manufactures gate, meaning...the timber was OK when it left his facility?
Is there a different regulation stating that timber needs to be HT treated AND below 20%MC to prevent fungal growth at time of leaving the manufacturing facility?

[StavrosA]

Here are the details in a simple way: heat treatment just kills the bugs thus pasteurizing wood (like with your milk that will go bad after few days, regardless). HT does not protect wood from future attacks by fungi unless the temperatures reached during HT are above 150C where they change the chemistry of wood thus making "unattractive" to fungi. 

Fungi need 4 things to thrive, namely, good food (wood itself that is not chemically poisoned), oxygen, good temp and moisture above 30%. Take away one of those 4 things and fungi stop grow.

Therefore, if HT treated wood gets wet in the future and the wood (food) is not "poisoned" (toxic chemicals inside it), fungi will come back sooner or later.