Table of Contents
Introduction
Fumigation is a routine operation when transporting bulk agricultural goods. But occasionally, it can go horribly wrong ending in fire or explosion. That’s exactly what happened in a known case where a fumigation procedure triggered multiple explosions in the cargo holds.
In this article, we’ll walk through the explosion caused by the fumigation incident, understand how and why it occurred, examine the scientific hazards (gas chemistry, heat, ignition), and draw out lessons to prevent similar disasters. The aim: simple, practical, relevant for students and marine professionals alike.
The Incident: What Actually Happened
Loading & Fumigation Setup
A bulk carrier loaded yellow grain (corn) in all its cargo holds, filling up to the hatch coamings. After the loading was done, a team of fumigation technicians came aboard with fumitoxin (aluminum phosphide) pellets. The cargo documents required that these pellets be applied subsurface (i.e., beneath the top layer, distributed), not just sprinkled on top.
But instead of following that procedure, the technicians poured the pellets from flasks while walking on hatch covers or comings. This took a bit over an hour. After finishing, they closed all hatches, and the ship sailed.
Sequence of Explosions
A few hours into the voyage, one hold exploded. The crew noticed hatch covers had shifted, and blue-grey smoke was emanating along edges. About an hour later, another explosion occurred in a second hold; soon after, more explosions erupted in other holds. Essentially, explosions propagated across multiple holds.
This wasn’t a single isolated pop, it was cascading. The scale of damage included dislodged hatch covers, structural deformation, damaged hatch coamings, and smoke-blacked cargo surfaces.
Scientific & Technical Causation
To appreciate how a fumigation can lead to explosion, a bit of chemistry is unavoidable.
Aluminum Phosphide → Phosphine Gas
Fumitoxin pellets (and many fumigants) contain ~55% aluminum phosphide (AlP). When AlP contacts moisture, it reacts to release phosphine (PH₃) gas (plus heat).
Phosphine is toxic, flammable, and under certain concentrations, explosive. The lower flammable (explosive) limit is about 1.8–2% by volume in air. Beyond that, a phosphine-air mixture can ignite or explode.
In this incident, the gas concentration in each hold exceeded that lower flammable threshold.
Improper Pellets Distribution & Heat Buildup
Because the fumigation pellets were poured on top (rather than subsurface or evenly) they tended to cluster in small pockets. In these clusters, moisture contact is more intense, accelerating the reaction and producing excess heat and gas in concentrated pockets.
Additionally, if there is condensation, cargo sweat, or free water in contact with pellets, the reaction accelerates further, increasing risk.
The heat from clustered reactions can ignite adjacent cargo or packaging (bags, paper). This heat + flammable phosphine mixture enables an explosion.
Ignition Sources & Auto-Ignition
Phosphine (especially impure) may ignite spontaneously under certain conditions. Some possibilities:
- Impurities like diphosphine can trigger spontaneous ignition at ambient temps.
- The reacting pellets themselves may reach temperatures above auto-ignition thresholds (pure PH₃ ~38 °C, impure ~150 °C).
- Heat from smoldering cargo or electrical sources (lights, fans, sparks) may ignite the gas.
- Non-intrinsically safe lights or fans left switched on inside holds can act as ignition sources.
If an explosive flame propagates through the headspace mixture, it causes a volume explosion, raising pressure enough to jerk up hatch covers or damage bulkheads.
Broader Risks & Similar Cases
This is not isolated. Similar incidents and warnings have been documented:
- The Swedish P&I Club’s safety scenario echoes nearly identical facts: misdistributed fumigation pellets, progressive explosions across holds.
- Safety4Sea (maritime safety portal) has described “multiple explosions onboard after cargo fumigation,” identifying the same root causes.
- West P&I warns that improper setting of aluminum phosphide tablets (clusters) leads to fire or explosions.
- IIMS has highlighted dangers: cargo damage, fire, explosion, condensation issues in post-fumigation.
Also Read: Types of Commercial Ships in the Merchant Navy: A Complete Guide
Lessons & Preventive Measures
From this incident and related analysis, here are clear lessons and safety measures:
1. Strict Adherence to Fumigation Procedure
Apply fumigants exactly as per cargo documents and manufacturer instructions. If subsurface placement is prescribed, do not shortcut.
Avoid piling pellets on the surface; prevent clustering. Even dispersion is safer.
2. Consider Cargo Moisture & Weather Conditions
High humidity, sweat, condensation or water ingress accelerates the AlP reaction. Cargo moisture content must be assessed before fumigation.
Ensure holds are dry, hatch covers are weather-tight, no ingress of rain or seawater.
3. Ventilation & Controlled Timing
After fumigation, holds are typically sealed for some time before ventilation. But ventilation must eventually happen to remove residual gas. If done improperly, condensation, sweating, or residual gases accumulate and increase hazards.
4. Gas Monitoring & Temperature Checks
Ships should carry gas detection equipment (for phosphine, O₂, flammable gas) and infrared thermometers to spot “hot spots” on hold steelwork.
Monitor gas levels periodically. If levels approach LEL, take action.
5. Eliminate Ignition Sources
Before fumigation, isolate all electrical devices (lights, fans) in holds or ensure they are intrinsically safe. Sparks or heat sources must be avoided.
Ensure no switches, wiring faults, or hot surfaces inside holds.
6. Crew & Management Training
Ship operators, crew, and fumigation contractors must be trained in fumigation risks, chemical behavior, procedures, emergency measures.
The management should enforce audits, checks, and compliance culture.
7. Use Proper Fumitoxin Tools & Documentation
Follow manufacturer’s MSDS and instructions. The MSDS must be onboard and reviewed.
Residues must be handled with care; unreacted residues can ignite spontaneously if stored together.
8. Seek Specialist Advice in Emergencies
If anomalies are seen (smoke, heat, hatch movement), expert guidance should be sought early. Some actions (opening holds) may worsen the situation.
Practical Scenario: “What Would I Do If I Face This Onboard?”
Putting yourself in the crew shoes:
- Before fumigation, review cargo docs, MSDS, weather, moisture.
- Vet the fumigator team: ensure they know correct procedures.
- Oversee application: ensure pellets are spread evenly or subsurface.
- Seal and monitor gas evolution (without entering holds).
- Use gas detectors and IR thermometers to catch hotspots or flammable levels.
- If smoke or heat arises, DO NOT open hatches immediately — isolate, ventilate carefully, call experts.
- Ensure all crew are clear of holds during fumigation and until safe gas levels are confirmed.
Conclusion
This case of explosion caused by fumigation is a potent warning. A chemically simple reactant (aluminum phosphide) became an agent of destruction when misapplied. Heat, gas buildup, ignition sources all conspired.
But it’s not magic. The hazards are known. The precautions are known. What makes the difference is discipline, training, procedural rigor, and respect for chemical danger.
The next time fumigation is scheduled onboard, this story should serve as a mental red flag: one small mistake in placing pellets, or ignoring moisture, or leaving lights on can turn safe cargo into an explosive trap.
