Understanding Spontaneous Combustion in Stored Hay: Prevention and Management

Spontaneous combustion in stored hay is a critical issue for farmers and can result in devastating losses. This phenomenon occurs when internal heat builds up due to microbial activity and chemical reactions within the hay, reaching the point of ignition.

Understanding the Process of Spontaneous Combustion

Unlike fires that result from external factors such as lightning strikes or machinery malfunctions, spontaneous combustion is particularly insidious. It often begins deep within a haystack, smoldering unnoticed until it bursts into flames.

How Does Spontaneous Combustion Occur?

Hay, an organic material, is rich in sugars, proteins, and moisture—ideal conditions for microbial growth. When hay is baled while still wet or before it has fully cured, the breakdown of plant matter by bacteria and fungi generates heat, raising the risk of ignition.

Key Risk Factors

• High Moisture Content: Hay with moisture levels exceeding 20% is at risk. Mould growth and potentially dangerous fermentation occur between 20-35% moisture.
• Dense Packing: Tightly packed bales trap heat and moisture, accelerating microbial growth.
• Poor Ventilation: Lack of airflow hinders heat dissipation.
• Environmental Conditions: Warm, humid weather increases risk.
• Poor Storage Practices: Enclosed barns or sheds without monitoring are particularly hazardous.

Signs of Heating Hay

Early detection of heating can save lives and resources. Farmers should actively inspect haystacks for:

• Steam rising from the stack
• Unusual musty, caramel, or tobacco-like odors
• Mould growth on or inside bales
• Condensation or rust under roofing
• Visible slumping or deformation of the stack

A metal rod (like a crowbar) or a temperature probe can help identify heat within the haystack. If the metal feels hot after removal, immediate action is necessary.

Preventing Heating in Hay

To minimize the risk of spontaneous combustion, it’s crucial to:

• Allow hay to dry completely before baling and monitor moisture levels with a moisture meter.
• Maintain ideal moisture content: 18-20% for small square bales, 12-15% for large square bales, and 15-18% for round bales. Thoroughly check plant nodes and leaf sheaths for concealed moisture.
• Utilize temperature probes or wireless sensors to monitor internal bale temperatures, adjusting management practices accordingly.
• Store hay in well-ventilated areas and avoid tight stacking to promote airflow.
• Keep damp or potentially suspect bales separate and monitor them closely.
• Use smaller stacks to reduce heat buildup and leave spaces for airflow.
• Ensure proper roofing and drainage to protect hay from moisture.

Actions to Take if Hay is Heating

• Disassemble the haystack to release heat and moisture.
• If safe, move bales outdoors.
• Call emergency services if smoke or flames are visible.
• Keep fire suppression tools like hoses and extinguishers readily accessible.

Never attempt to extinguish a hay fire alone as it can quickly reignite and spread.

Conclusion

Spontaneous combustion is a preventable issue in hay management. By understanding its underlying biological and chemical processes, farmers can adopt proactive measures to safeguard their property and livestock. Proper curing, continuous monitoring, and sound storage practices are key to ensuring safe hay management.

For more information about drought support, visit www.agriculture.vic.gov.au/drought.

Source: Agriculture Victoria