Ministry of the
Solicitor General

OFM - TG-03-1998: Storage of Wood Chips

OFM Guideline

Office of the Fire Marshal

OFM logo



October 1998

The reproduction of this guideline for non-commercial purposes is permitted and encouraged. Permission to reproduce the guideline for commercial purposes must be obtained from the Office of the Fire Marshal, Ontario.









The outdoor storage of wood chips requires certain fire protection measures in order to prevent a potentially serious fire hazard. Wood chip piles have the potential to heat internally and spontaneously combust if not managed correctly. The Ontario Fire Code addresses the outdoor storage of wood chips in Subsection 3.2.3.


This guideline discusses the cause of internal heating and some of the factors that increase the potential for a spontaneous fire in wood chip piles of different composition. Recommendations, in addition to the Ontario Fire Code requirements, are included.



This guideline is intended to assist fire officials in assessing the potential hazard of the outdoor storage of wood chips and the appropriate measures that must be taken in order to mitigate the hazard. The guideline is applicable to various places where the outdoor storage of wood chips may be present including, but not limited to, recycling facilities and community parks.



The 1998 Ice Storm in Eastern Ontario produced a large amount of debris from damaged and downed trees. Wood chippers have been used to reduce the debris into more manageable wood chip piles. However, wood chip piles pose a potential fire hazard if not managed correctly.

Generally, outdoor wood chip piles contain a high moisture content and are not usually susceptible to surface fire ignition. On the few occasions where surface fires have occurred, it has usually been caused by exposure to another fire or from equipment working on the piles. Once a surface fire has been initiated the fire could produce tremendous heat especially during dry weather conditions with winds in excess of 30 km/h.

Internal fires are much more common than surface fires and are difficult to detect and extinguish. Such fires are capable of burning for extended periods before any obvious indications of a fire are observed. Spontaneous heating is caused when heat produced by the microbial decay of wood is not readily dissipated. Pile temperatures can reach a temperature of 66°C after two weeks. In some piles, the temperatures continue to rise due a number of factors. These factors include the pile height, a low surface-area-to-volume ratio, the age of the wood chips (older and more compacted), low air flow, and the presence of impurities such as bark, decayed wood, and sawdust. Fires frequently occur while attempts are made to separate heated from non-heated chips. When heated chips are exposed to sufficient air, combustion may occur.

Blown wood chips or pneumatically conveyed wood chip piles are more vulnerable to spontaneous combustion since the fines are separated and stratified in such a manner that hampers heat dissipation.



The Ontario Fire Code (OFC) addresses the outdoor storage of wood chips in Subsection 3.2.3. as follows:

Deviations from requirements This Subsection does not apply where the existing situation is approved and does not endanger life safety, or approved alternative measures to the requirements set out in this Subsection are taken to provide life safety.

Note: "approved" means acceptable to the Chief Fire Official.

Surface of ground The storage site shall be well drained and be level, solid ground or paved with asphalt, concrete or other hard surface material. The ground surface between piles shall be kept free of combustible materials.

Vegetation removal Weeds, grass and similar vegetation shall be removed from the yard.

Burning of weeds

(2) Portable open-flame weed burners shall not be used in chip storage yards.

Pile dimensions

* Piles shall not exceed 18 m in height, 90 m in width and 150 m in length unless temporary water pipes with hose connections are laid on the top surface of the pile.

Fire department access Space shall be maintained between chip piles and exposing structures, yard equipment or stock equal to

(a) twice the pile height for combustible stock or buildings, or  

(b) the pile height for noncombustible buildings and equipment.

(2) Despite Sentence (1), space between chip piles and exposing structures, yard equipment or stock shall not be less than 9 m.

* Where storage areas are fenced or otherwise enclosed, gates at least 3.5 m in width shall be provided to permit entry of fire department vehicles.

* Permanently installed access walkways at least 1.8 m wide and constructed of noncombustible material shall be provided so that hose streams may be directed on any part of the piles.

(2) Despite Sentence (1), other approved means may be used to ensure adequate fire department access to the piles. Piles exceeding 150 m in length shall be surrounded by fire department access routes at least 9 m wide.

Smoking prohibited Smoking shall be prohibited in chip pile areas.

Fire extinguishing provisions Portable extinguishers for Class A fires shall be provided on vehicles operating on chip piles in addition to the units for Class B fires normally required for the vehicles.

* Hose houses or cabinets shall be provided around the perimeter of chip piles at intervals not exceeding 120 m.

*(2) One 75 m length of 65 mm hose and 2 portable extinguishers having a 2A or higher rating and conforming to Section 6.2 shall be installed in each hose house or cabinet.

*(3) Each hose required in Sentence (2) shall be connected to a water supply capable of supplying 1140 L/min of water to it at a pressure that will allow the hose stream to reach the top of the chip pile.

* Portable extinguishers in conformance with Section 6.2 shall be provided in transfer houses.



It may be difficult to comply with all the requirements listed in the Ontario Fire Code due to the nature and location of the piles. The wood chips produced from the debris in Eastern Ontario is of a different composition than those found in pulp and paper mills or similar operations where the chips are of a homogenous composition. The requirements listed in Subsection 3.2.3. of the OFC are intended for wood chips of good quality. The wood chips resulting from the ice storm cleanup will contain bark and other impurities that cause the chip piles to be more susceptible to internal heating.

Some wood chip piles are located in public parks and other temporary storage locations. Where compliance with the prescriptive provisions of the OFC is not practical, Article permits the Fire Department to accept alternative measures to provide an equivalent level of life safety.

The following recommendations should be considered as compensating features when dealing with these types of wood chip piles, particularly for items identified by "*" in section 3 of this guideline.

  1. The maximum storage period for these wood chip piles should be no longer than 3 months. It should be noted that some piles in Eastern Ontario that have been in existence for 3 months have already shown signs of spontaneous combustion. If the storage period exceeds 3 months, the recommendations as noted below in item No. 4 should be implemented.
  2. Compaction of the pile should be avoided.
  3. The piles should be periodically wetted down, especially during dry conditions, to minimize the possibility of a surface fire. If this is undertaken, it must be done on a regular basis.
  4. The maximum height of the wood pile should be 7.5 m. The OFC allows a pile height of 18 m but Factory Mutual1 recommends that the height be limited to 7.5 m due to the inclusion of tree bark and other impurities in the wood chips.

If the storage period is expected to exceed 3 months, then the overall dimensions of the pile should be decreased. In such cases, the maximum height at the peak of the pile should be 4 m and the width at the base should be no more 8 m. These piles should be limited to a maximum bulk volume of 1,000 m3 . A pile with a height of 4 m, a base width of 8 m and a volume of 1,000 m3 should have a length of 67 m. It is recommended that these piles be formed in a triangular shape with 45° side slopes. Fire department access must still comply with Article where the distance between piles shall be no less than 9 m.

  1. If a hot spot is detected, water spray or fog coverage should be provided while the pile is dug out. An alternative is to use perforated piping to flood the hot spot with water before uncovering the pile.
  2. Prepare a pre-fire plan that, at the very least, includes the following information:
  • Emergency procedures to be used in case of fire,
  • Procedures for notifying the fire department ,
  • Detailed maintenance procedures and instructions on fire prevention methods for the control of fire hazards (example: items No's. 1 and 3),
  • Information regarding supervisory staff including their related fire safety duties and responsibilities,
  • Instructions and schematic diagrams describing the type, location and operation of fire emergency systems (example: location of closest hydrant or water supply, site plan).

[1 Factory Mutual Loss Prevention Data 8-27, December 1980, Storage of Wood Chips]