Heat Treatment Guide for Firewood

Prior to the heat treatment certification test and thermal mapping process for a new or existing facility, a detailed work plan of the facility’s physical characteristics and a written, step-by-step description of all the processes related to treatment must be approved by the agency officials.

At a minimum, work plans must include a description of all processes related to the heat treatment of firewood. These descriptions should reference diagrams with numbers where appropriate. 

The process of reviewing the work plan may take up to 20 days. Additional information requests may extend this time. Facilities should take this time constraint into account when developing a project timeline. Work plan approvals expire one year from the approval date, if the facility has not been certified.
 

Following work plan approval, facilities seeking certification must be tested by an agency official to ensure the facility can meet all treatment requirements. If deviations from the approved work plan are necessary, the certifying agency must approve these changes in the work plan prior to testing. A certification treatment test must be completed for each chamber load and volume configuration.

The required number of permanent sensors for normal operation of the facility depends on factors such as the chamber size, chamber dimensions, and air flow patterns. See Table 1 under Certification Treatment Test Requirements to determine how many permanent temperature probes are needed.

All sensors should be placed in the largest firewood piece in a portion of the load. The sensor portion of the probe should be fully embedded in the pre-drilled holes to measure internal wood temperature. Sensors are to be sealed into each hole with non-hardening putty to prevent reading ambient air temperature. Other recording arrangements may be considered if approved by the certifying agency.

The agency official will use the agency-owned portable sensors, in addition to the facility’s permanent sensors to conduct the certification treatment test. This test detects the coldest area in the chamber and is also referred to as thermal mapping. The agency official will place portable temperature sensors throughout the chamber and temperatures will be automatically recorded at a specified time interval. A tamper resistant seal will be placed on all doors by the agency official. The tamper resistant seal(s) must not be removed, altered, or mutilated in any way except in the presence of the agency official. Breaking the seal and tampering with the treatment chamber will invalidate the test treatment. After the treatment has been completed, the company will notify the agency official.

The sensors that require the longest time to record the approved treatment temperature represent colder areas of the chamber. The certification treatment test must be conducted with the kiln loaded the way the facility plans to use it, as stated in the approved work plan. The agency official chooses which pieces of wood to place the probes into, and where to place those pieces of wood in the kiln.

In certain situations, the thermal mapping may be conducted separately from a certification test treatment.

These certification test treatments should test the ability of the treatment chambers to heat a standard load of wood according to the treatment guidelines. The company’s facility sensors must be located in areas specified by the certifying agency. The company must maintain the placement and monitor sensors in these locations for all certified heat treatments. Bent sensors may not read properly and must be replaced. All damaged sensors must be replaced with temperature sensors from the manufacturer or a temperature sensor that has been certified by the National Institute of Standards and Technology (NIST) within the last 12 months.

If the data shows that the test treatment failed, any problems or deficiencies found in the facility or with the treatment must be corrected by the facility, and the facility must modify their work plan to reflect these corrections. Then the agency official will run the test treatment again, until all treatment requirements are met and the facility passes.

A certification test performed by an agency official is required once a year for non-commercial heat treatment facilities, or whenever the system has a malfunction, breakdown, or other failure that requires modifications that alter the way the system functions. This excludes the replacement of a faulty temperature sensor if either the replacement temperature sensor is new from the factory, or the sensor had been NIST certified within the past 12 months.

The facility shall be considered certified only after the state is paid in full for certification services.
 

All facility temperature sensors must be calibrated annually, at the discretion of the certifying agency, or whenever any part of the temperature recording system fails or is replaced. Calibrations must be performed by trained technicians to National Institute of Standards and Technology (NIST) standards. The MDA may request the NIST certificates for the facility at any time.

Once the facility is approved, the facility is required to sign a compliance agreement with the certifying agency, with the work plan attached as an addendum. See Guidance Document 3 for more information about Compliance Agreements.

A certificate will be included in the compliance agreement, which must be used in the manner described under the Documentation section.
 

All use of the MDA issued heat treatment certificate must be thoroughly documented including:

• Date(s) of treatment
• Printed name and signature of person certifying treatment
• Destination of treated firewood*
• Date(s) of shipment of treated firewood**
• Certificates must be accompanied with the point of origin and final destination clearly indicated on the bill of lading or other shipping documents

All firewood sold by an MDA certified company must be clearly labeled with the following information:

• Company name
• Business address or website
• County and state of harvest
• Net quantity in volume or weight
• MDA Certified Safe to Move Logo
• All firewood labels must be in compliance with Minnesota Statutes 239.092 and 239.093 as applicable.

*The destination of treated firewood may by coded by the company using a unique identifier. However, in the event of a failed heat treatment, failed inspection, or revocation of the certificate, the company must supply the MDA with a complete list of unique identifiers and corresponding company information.

**In the event of a failed inspection or revocation of the certificate, the MDA reserves the right to request information regarding the destination and shipment dates of all firewood, regardless of whether it was heat treated or not.

1. Business name
2. Business owner name
3. Business phone number(s)
4. Email address(es)
5. Business website
6. Business address
7. Heat treatment facility address (if different)
8. Storage facility address (if different)
9. Applicant’s interest in property if other than owner
10. GPS coordinates for each address, or locations marked on a USGS topographical map with identifying labels
11. Heat treatment facility make and model (if commercially built or designed)
12. Temperature probe and data logging equipment make and model (required if heat treatment facility is not commercially built)
13. Description of crates, bins, racks, etc. used to hold firewood during treatment, including total volume and projected capacity
14. Description of the process used to calibrate the temperature sensors, and how the calibration will be documented (must be calibrated by a lab or technician with NIST certification)
15. Description of the post-treatment packaging
16. Procedures to prevent re-infestation of treated wood (if receiving wood from or located in a spongy moth quarantine area)
17. Treatment chamber details, including heating system, arrangement within the chamber, and airflow (include a diagram of the interior setup of the heat treatment facility)
18. Map of facility, with all landmarks uniquely labeled. Map should include at least:
    • North arrow
    • Scale (if available) or statement that the map is not to scale
    • Heat treatment facility
    • Arrival and storage of untreated wood
    • Storage of treated wood
    • Delivery pickup area for treated wood
    • Delivery pickup area for untreated wood
    • Any other relevant landmarks
19. Copy of label on firewood bundle. Label must:
    • Be legible
    • Follow all state labeling requirements in Minnesota Statutes Sections 239.092 and 239.093
    • Allow space for a certificate shield (1.5 inches by 1.5 inches)
20. Specified location for record storage (records must be kept for 24 months)
21. Template record for each firewood treatment, including:
    1. Business name
    2. Business phone number(s)
    3. Business address
    4. Date of treatment
    5. Unique lot number assigned
    6. Volume treated in lot number
    7. Treatment record showing time and temperatures
    8. Storage area before shipment
    9. Date of shipment
    10. Receiver of shipment, including name and full address

The number of temperature sensors depends on the size of the treatment chamber.

Table: The number of temperature sensors required per load will vary with the internal size of the treatment chamber. The minimum requirement is four (4) sensors – one (1) for measuring air temperature and three (3) for measuring internal wood temperature. For loads greater than 5,000 ft3 (142 m3) of wood, a minimum of one additional sensor for measuring internal wood temperature must be provided for each additional 2,000 ft3. For example, a load of 9,000 ft3 would require a total of six (6) sensors (one ambient air temperature sensor and five [3 + 2] additional sensors).