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Spontaneous Combustion

Spontaneous Combustion
“Safety Moments, presented at CCA Stations and Posts”
By Chuck Hawley, San Francisco Station, August 2023

The story in MarineLog on this year’s Summer Solstice seemed both familiar and odd at the same time. A yacht valued at $1,500,000 burned to the waterline, and later sank, while undergoing some routine maintenance at a marina in Washington state. Closed circuit cameras showed that around 2:00 am, the fire started in the cockpit, and then grew slowly over an hour or so before someone noticed it and called the fire department. By then, the yacht was engulfed in flames. Unfortunately, no one was looking at the camera feed until it was too late. Luckily, there were no injuries associated with the fire.

A report released by the NTSB pointed to “oily rags” as being the source of ignition. The workers on the boat had been applying a vegetable oil to the external wood on the day prior to the fire. The oil was linseed oil, used for ages to waterproof and protect exposed wood. Made from the ripened seeds of the flax plant, it’s been a common marine wood preservative along with tung and other natural oils. 
So what would make linseed oil a potential source of ignition on a boat? Getting linseed oil to burn requires three ingredients: the oil itself or one of many organic vegetable or animal oils (not petroleum oils, paradoxically), insulation like an application rag, and oxygen. Heat is generated when a double (or triple) atomic bond in the oil is broken which releases a small amount of energy, and thus the heat. The insulation causes the heat to be confined and not dissipate to the environment. Over time, the oily rags increase in temperature, until they reach the ignition point for the particular oil, and a fire starts.
Petroleum oils are considered “saturated” and have single bonds. The single bonds are not subject to breaking and releasing heat, although they are obviously sources of energy (fuel) when heated from an outside source to their ignition point. The chemistry of the natural oils allows them to generate their own heat from the oxidation due to their “unsaturated” double and triple bonds.
Many other oils other than linseed oil have this property, including castor oil, cottonseed oil, fish oil, olive oil, peanut oil and soybean oil, but those are less likely to be used in boat maintenance, and are therefore not the focus of marine fires. 
Incidentally, you can also have spontaneous combustion from biological processes, like those that occur when compost catches fire. Anyone who has worked on a ranch or farm has seen steam swirling up from piles of compost or manure in the morning which can also generate enough heat to cause a fire. Boat owners are not likely to have sufficient compost onboard to be in danger from this source of fire.


The Cruising Club of America is a collection of accomplished ocean sailors having extensive boat handling, seamanship, and command experience honed over many years. “Safety Moments” are written by the Club’s Safety Officers from CCA Stations across North America and Bermuda, as well as CCA members at large.  They are published by the CCA Safety and Seamanship Committee and are intended to advance seamanship and safety by highlighting new technologies, suggestions for safe operation and reports of maritime disasters around the worl