Used to be you could just grab a wooden pallet and use or reuse it as a pallet, or tear it down to the slats and rails and use the lumber for other projects or as kindling to start a fire. Not any more.
There is the logo of the International Plant Protection Convention (IPPC) and is stamped on the wood of the pallet.
IPPC pallets are used for international shipping and require require pallets constructed using raw wood to be treated and to be made of a material that will not carry invasive insect species or plant diseases through different countries. Officially approved agencies supervise pallet treatment methods.
There are other markings beside the logo that you want to look for.
[HT]: Wooden pallets manufactured in Canada or the US undergo a pest control treatment called heat treating (HT) which involves heating the pallet to a minimum core temperature of 56°C (133° F) for softwoods and 60°C (140° F) for hardwoods for a minimum of 30 minutes in a kiln. HT pallets are not harmful to your health.
[KD]: The purpose of kiln-dried lumber is to reduce the moisture content of the wood (19% or less). This is a means to control warping, fungal growth, and other quality features. The kilns or ovens used to dry the wood do not necessarily reach the sustained temperature of 133 degrees Fahrenheit (56 Celsius) that would qualify as heat treated. Many lumber mills are processing their timber to meet the heat treatment requirements; thus you will see “KD-HT” incorporated in the wood grade stamp.
With cherry and oak wood, the curing temperature causes releases sap from within the wood. Sap coats the wood with a dark stain, making the pallets or crates appear old and worn. The heat treating process does not compromise the strength and durability of pallets and containers. KD pallets are not harmful to your health.
[DH]: New, used, previously assembled, repaired, or re-manufactured wood packaging material is heat treatment using dielectric heating.
[DB]: These two letters indicate that the pallet is debarked according to IPPC regulations. Many pallets have this stamp. It does not matter if your pallet has this stamp or not. Many pallets do not have it.
The process of “debarking” wood is to remove the bark (rough outer layers of wood) using a cutting tool or a planer, and the pallet wood remains untreated. This procedure is done to allow for a more thorough treatment of wood before being approved for transport (aside from smoothing the wood). Pallets marked with the letters DB only are chemical-free and safe to use. Newer pallets no longer require this stamp by the IPPC, as most modern wood treatment procedures require “debarking” as a standard part of their process.
Avoid “HIGHLY TOXIC” pallets! MB pallets. They are not Safe!
[MB]: Methyl bromide (Bromomethane) fumigation, this is a potent pesticide linked to human health problems and ozone layer depletion. Methyl bromide fumigation kills invasive species like pine beetles.
In 1987, the Montreal Protocol aimed to regulate the use of methyl bromide, along with multiple other chemicals found to impact the ozone. This type of treatment is now banned in Canada and many countries because it poses health risks to workers handling the pallets. However, you can still find it in some places. If you find an MB pallet (likely from Asia or Oceania), do not use it for your craft projects or as firewood, find a waste-removal company that can dispose of it properly.
MB pallets are not Safe! Reference Toxipedia, Methyl bromide
Methyl bromide is a broad spectrum pesticide used to control pest insects, nematodes, weeds, pathogens, and rodents. In the U.S., methyl bromide has been used in agriculture, primarily for soil fumigation, as well as for commodity and quarantine treatment, and structural fumigation.
Methyl bromide can enter the body through inhalation by breathing air contaminated with methyl bromides, through the skin or the eyes. The symptoms of inhalation of methyl bromide are abdominal pain. convulsions, dizziness, headache, labored breathing, vomiting, weakness, hallucinations, loss of speech and in-coordination
When skin comes in contact with methyl bromide, it can cause itching, burning, and tingling. Skin absorbs methyl bromide and it causes the following symptoms redness, burning sensation ,pain and blisters
When methyl bromide comes in contact with eyes, the symptoms are redness, pain, blurred vision, temporary loss of vision
The EPA lists methyl bromide as “highly acute toxic“! Methyl bromide has not been used since 2005 in most countries, but there are still old pallets in circulation.
References: IPPC, IPPC WHO, Wood Packaging for Export, FAO UN, FAO UN2 CFIA, Pallets. Toxipedia, Biological Invasions, Plant Quarantine, ISPM 20 Guidelines, Methyl bromide, Bromomethane, Methyl bromide 2, ATSDR-MMG, and others