Spontaneous combustion or chemical reaction

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Report: NFPA's "Fires Caused by Spontaneous Combustion or Chemical Reaction"
Author: Ben Evarts
Issued: November 2011

This analysis of fires with "spontaneous combustion or chemical reaction" listed as the heat source includes information on incident type, and where and when the incidents occurred.  lso includes selected published incident descriptions.

Executive Summary

Fires caused by spontaneous combustion or chemical reaction accounted for an estimated average of 14,070 fires per year between 2005 and 2009. These included 3,200 structure fires, 1,150 vehicle fires, 5,250 outside non-trash and unclassified fires, and 4,460 outside trash or rubbish fires. The most common occupancy types for structure fires were residential (50% of fires), storage (12%), mercantile or business (9%) and manufacturing or processing (9%). Because the fires are coded as "spontaneous combustion or chemical reaction" there is no way to determine what the exact circumstances were (spontaneous combustion versus some other kind of chemical reaction). 

Spontaneous combustion is a byproduct of spontaneous heating, which occurs when a material increases in temperature without drawing heat from its surroundings. If the material reaches its ignition temperature, spontaneous ignition or combustion occurs. Examples of materials that are prone to spontaneous combustion include: oily rags, hay, and other agricultural products. 

The statistics in this report are derived from the United States Fire Administration’s National Fire Incident Reporting System, (NFIRS), as well as the NFPA annual survey. NFIRS provides the details of fires, and has a code for the “heat source” field which is “Spontaneous combustion, chemical reaction”. Because “spontaneous combustion” cannot be separated from other chemical reactions, some fires not caused by “spontaneous heating” are included, but analyzing fires coded this way still gives insight into the problem of spontaneous combustion.

In home structure fires (homes are defined as one- and two-family homes, apartments, and manufactured housing), the garage was the most common area of origin (20% of fires) and oily rags were the most common item first ignited (35%). Abandoned materials were cited as a factor in 34% of home fires, and improper containers or storage was a factor in 33%.

In storage properties, the most common structure use was an outbuilding or shed (35% of fires). Oily rags were the item first ignited in 22% of storage property fires, and agricultural crops, including fruits and vegetables, were first ignited in 20%.  

One-quarter (25%) of such fires in mercantile or business properties fires occurred in laundry or dry cleaning occupancies. These fires in mercantile and business properties were less common during “business hours” between 9:00 a.m. and 6:00 p.m. Oily rags were the item first ignited in one-third (34%) of these fires. Improper containers or storage was cited as a factor in 35% of these fires.

Fires caused by spontaneous combustion or chemical reaction in manufacturing properties were more common between 6:00 p.m. and midnight. Oily rags were the item first ignited in one-quarter (26%) of fires, and rubbish, trash, or waste was the item first ignited in 11%. 

Half (50%) of the vehicle fires caused by spontaneous combustion or chemical reaction occurred in passenger vehicles. The 16% of fires that occurred in a road freight or transport vehicles caused 25% of the direct property damage. More than one-third (36%) of vehicle fires began in the trunk or cargo area of the vehicle. One-fifth (20%) of these fires began with flammable or combustible liquids or gases, piping or filter. Nineteen percent began with oily rags.

Outside and unclassified fires (excluding outside trash or rubbish fires) were more likely to be reported during the warmer months and in the afternoon hours (between noon and 6:00 p.m.). Unclassified organic materials were first ignited in 28% of fires, and 26% began with light vegetation, including grass. 

Outside trash or rubbish fires were more common during the warmer months (peaking in July), and in the afternoon and early evening hours. Unsurprisingly, the leading item first ignited in these fires was rubbish, trash or waste (22% of fires), followed by oily rags (16%). Abandoned or discarded materials or products was a factor in four-in-ten (41%) of fires of this type.

How can spontaneous combustion be prevented? 

Agricultural products: Spontaneous heating in agricultural products can be prevented by control of moisture. Proper drying and adequate airflow will limit heating. Regular checks of temperature should be made.

Oily Rags: Rags that have absorbed oils such as linseed oil or turpentine should be kept in well-covered metal cans and thoroughly dried before collection or transport.1

1Fire Protection Handbook. 20. 1. Quincy, MA: National Fire Protection Association, 2008. 6-288 – 6-292. Print