Self-Heating and Spontaneous Combustion
Materials that may catch fire by spontaneous ignition are:
- Rags and waste with oil and paint residues
- Towels and linen during laundering and drying
- Paint overspray or material from a paint spray booth
- Coal
- Haystacks
- Green waste piles and compost
- Chemical substances such as cellulose nitrate
Spontaneous ignition occurs when a combustible material heats to its ignition temperature through a chemical reaction with oxygen in the air. Oxidation of the material generates heat, which, if not dissipated, accumulates until ignition occurs. This typically happens when materials are piled, trapping heat.
For ignition, air movement must provide enough oxygen for oxidation without cooling the material. This delicate balance makes spontaneous ignition uncommon but still a significant risk. Fires often occur after years of unsafe practices.
The risk increases in warm, dry conditions, like an Adelaide summer, as preheating accelerates oxidation and ignition.
While oil-soaked rags ignite less frequently now due to acrylic paints, the problem persists with oil-based paints, stains, and polishes. Linseed oil is the most common drying oil involved, but others like rapeseed, cottonseed, peanut, corn, and safflower oils may also self-heat.
Fish oils are particularly prone to self-heating, while mineral oils (e.g., white spirit, mineral turpentine, lubricating oil) are not and do not cause spontaneous ignition.
Preventing Spontaneous Ignition
- Store materials susceptible to self-heating in sealed metal containers like safety cans or bins. While these containers initially contain oxygen, the oxidation process will deplete it, halting the reaction.
- Linseed oil-soaked rags or those with other drying materials should be either immersed in water or spread out to dry safely after use. For transport, seal such rags in metal containers.
Risks in Laundry Practices
- Heat Retention in Towels and Linens: Day spas, salons, and massage parlours often launder towels and linens in bulk. Prevent fires by running materials through a cooling cycle in dryers or spreading them in single layers to cool completely before folding or stacking.
- Oil-Contaminated Linens: Massage parlours, in particular, must take extra care with linens soaked in oils. Wash them immediately with appropriate detergents designed to break down oils and prevent buildup, which can increase ignition risk.
- Ventilation in Laundry Areas: Maintain good airflow in laundry rooms to prevent heat and moisture buildup, reducing the risk of spontaneous ignition.
Day Spas, Hair Salons, and Massage Parlours
- Proper Storage of Flammable Materials: Ensure that oils, including massage oils and hair treatment products, are stored in sealed metal containers. Oils can oxidise and self-heat, leading to spontaneous ignition if not stored correctly.
- Handling Soiled Linens: Towels and linens soaked in massage oils, hair products, or cleaning solutions should be washed promptly. Avoid stacking or storing them while damp, as residual oils can promote self-heating.
- Dispose of Used Applicators Safely: Items like oil-soaked applicators, cotton pads, and sponges should be stored in fireproof bins or sealed metal containers to prevent ignition risks.
Residue from oils (e.g., cooking or massage oils) on towels or linens can remain after washing and lead to self-heating during drying. Minimise this risk by:
1. Laundering with plenty of detergent and hot water.
2. Using a cooling cycle or spreading items to cool completely before folding or stacking.
