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By: June F Gonzales, RCrim, MCJE, CCTS, PGDip-SRM

LEAPS Academy Philippines


This paper explored the cause of holdover fires otherwise known as zombie fires in the context of Philippine experience at Silay City, Negros Occidental, Philippines. It presented the combustible and explosive nature of solid organic and non-organic waste incidental in the production of sugar and the hazards inherent in the dumping of untreated effluents and sludge through the use of sludge drying beds.

This paper also discussed first-hand experience of locals who witnessed this strange occurrence as to how said holdover fires can stay dormant in the form of smoldering embers for weeks and months even. In addition, it explained how the holdover fire is ignited, from what substance does it subsist, how it behaves and its perceived resilience from extinguishment. It further covered the basic elements of fire and the actions taken by locals to mitigate its impact in the environment as well as actions taken by volunteers to combat the continuous spread of said holdover fire in said locality. It also shared the inherent hazards faced by sugar mills who are equally situated with waste disposal approach taken by AIDSISA sugar mill in the use of sludge drying bed to dispose of their organic and non-organic effluents which is a potential zombie fire awaiting favorable conditions for combustion. Finally, it pointed out the accumulation and storage of large quantities of dried organic and non-organic waste products for years in one area pose potential fire hazard if these hazards are not understood and no preventive and protective measures are installed.

ZOMBIE FIRE: The Phenomenon

Zombie fire is a new and catchier name for an old and relatively rare phenomenon. Known among Arctic fire managers as holdover or overwintering fires, zombie fires transcend the typical fire season. Holdover Fire or Zombie Fire is a fire that remains dormant for a considerable time.

In an article entitle Fire and Explosion Hazards of Sewage Sludge by SJ Manchester, he raised the issue of dust explosibility and self-heating qualities of the sewage sludge produced by industries such as but not limited to sugar production. Since 1997 at least six (6) significant fire and explosion incidents at sites in the United Kingdom and throughout Europe resulting in damage to equipment. These risks could have been prevented if the risk have been understood and adequate preventative and protective measures have been undertaken.

ZOMBIE FIRE: The Philippine Experience

In the Philippines, the locals of Barangay Sunrise, Silay City, in the Province of Negros Occidental have experienced a curious case of Zombie Fire, which occurred at a dried-up sludge drying bed of AIDSISA Mill located at Silay City, 25 kilometers north of Bacolod City. AIDSIA short for Agro-Industrial Development of Silay-Saravia was once a flourishing Sugar Mill, has a waste water treatment pit where sludge and other organic and non-organic materials incidental in sugar production are dumped in a man-made pond. The sugar mill has long been gone, its equipment either sold as second-hand units or as scrap iron. What is left is the vacant area which for a time was full of production activity, since 1972 to about 2000.

When the sugar central came to a close due to bankruptcy, the said waste water treatment pond dried up. With neglect, the drying and absence of protective and preventive measures opened the pit to a host of hazards, one of which is the occurrence of holdover fire or zombie fire. This occurrence usually take place during the summer where the heat is ideal for combustion. Strange as it may seem, the fire would keep smoldering eating up what it can as it burrows down to the ground and it would smolder as it gets deeper into organic deposit in the pit. Inch by inch it advances everyday generating smoke and heat posing a question of how a fire can last for weeks, months even without being extinguished.

Combustible and Explosive, Nature of Sugar Processing Byproducts

Research disclosed that these holdover fires are directly attributable to the process of sugar production. Sugar industry is one of the important agro-based industries in the Island of Negros. The industry has created significant socio-economic impact on rural agro-based economy in particular. The residues from sugar are part of the natural products. A large volume of waste of organic nature is produced during the period of production, and normally they are discharged onto land or into nearby watercourses, usually small streams, practically without pre-treatment.

A Sludge-drying bed provide the simplest method of dewatering. A digested sludge slurry is spread on an open bed of sand and allowed to remain until dry. In the case of AIDSISA, a sludge drying pond became the ideal method to treat the waste incidental in sugar production. Picture out a man-made lake that contains all the sugar mill’s putrescible output and there left to dry. Drying takes place by a combination of evaporation and gravity drainage through the sand.

In the case of AIDSISA the wastewater effluents and sludge are pumped into a sludge drying pond. The effluents and sludge which have accumulated in the pond for more than 20 years and with layers and layers of organic and non-organic materials mixed in a volatile combination would cause the pond to catch fire. Effluent discharges from sugar mill constitute a number of chemical pollutants, such as oil and grease, carbonate, bicarbonate, nitrite, phosphate, in addition to total suspended solids, dissolved solids, volatile solids and scopes of other intoxicants. These contaminants make up the ideal combination of a type of fire that is very difficult to extinguish.

Favorable Conditions for Ignition

These conditions only become worse as the stream flow reaches a very low level and when enough dilution water is not available during the period of operation of the Sugar mills (early October to end of May or June) the pond dries. The summer heat causes the sludge in the pond to cake up and in the process produces fine dust. This dust is combustible due to its low auto ignition temperature and the possibility of a fire incident could not be discounted.

In the dewatering of sewage sludge, a large quantity of dust and final dried product is produced both of which are readily combustible. They will form the fuel in what is known as “Fire Triangle”. This refers to the necessary requirement for the fire to occur in any system. The first requirement is the presence of fuel, and in order for fuel to burn a sufficient quantity of oxygen is required. Finally, there must be an ignition source present of sufficient energy to ignite the fuel and oxygen mixture.

The dried-up sludge produces combustible solid. In the presence of sufficient oxygen and with numerous potential sources of ignition present in the process, there is considerable risk of an explosion or fire occurring. In the case of AIDSISA sludge drying bed, the temperature during summer would cause the combustible dust to catch fire, a fire too difficult to extinguish. Locals would describe the fire as if sleeping embers underground producing smoke and possible production of gasses such as carbon monoxide and oxides of nitrogen. As the ground bellows smoke, the fire burrows deeper and deeper into the pit eating whatever organic and non-organic fuel it can consume.

Firsthand Experience

Vicente Parreno, a resident of the area for more than 20 years, could still vividly recall how townsfolk would wonder how the fire would go on for months, emitting smoke. According to him, the fire would not flare up or conflagrate to other areas but only exclusively around the sludge drying bed. Believing that the fire could only last for weeks, he and the locals were amazed at how the smoke continued to bellow underground for months which alarmed the residents as it endangers locals and farm animals who may accidentally venture near the pit.

Jocelyn Fermo, a resident near the sludge drying pond could still recall seeing smoke bellowing from the said area lasting for months, said fire would seem to die down during monsoon season yet would reignite after the pond has dried up again. Sugar mill workers and farmers who reside in the area are bewildered at the strange sight of smoke and fire in the pit and are lost for words as to how it came to be.

Firefighting Response

Despite efforts of locals to douse the smoldering pit with water, the fire would still survive, it may die down for a while but would reignite weeks after. It would take the help of volunteer rescue workers to stop the said zombie fire by digging up trenches inside the pond thereby creating gaps in the organic and non-organic fuel and the ground soil of the pond. By separating the fuel from the burning embers, the locals have successfully isolated the fire, preventing further conflagration which led to its extinguishment.

Thru this, the zombie fire came to an end. Said area in the hinterland of Silay City is still under tight watch as the fire might reignite if conditions are favorable, either by summer heat or by lightning strike. The burning of garbage is discouraged near the area as it might trigger particles to ignite. Locals residing in the nearby pond would regularly conduct patrols to check for occurrence of zombie fires in the area.

Inherent hazard in Sugar Production

The curious case of Zombie fire in AIDSISA Sugar Mill at Silay City is not unique, considering that today Negros Island is home to thirteen (13) sugar mills. This realization of the dangers of dust explosibility and self-heating qualities on the sewage sludge of sugar mills puts their respective sludge drying beds as potential zombie fire waiting for combustion if these hazards are not understood and that no preventive and protective systems are installed.

An Issue Subject for Climate Change Studies

The zombie fire phenomenon seems to be unexplored in the Philippines. Given the threats posed by climate change, this can be a good research area among criminologists and security and safety professionals. Finding out the threats and risks of zombie fire presence, most particularly in places similarly situated with Negros Occidental, will significantly add on to the values of literature, and in the making of concepts and frameworks for security and resiliency management.



  • Zombie Fires Erupting in Alaska and likely Siberia, Signaling Severe Arctic Fire Season May Lie Ahead

  • Managing Explosive Dust Risk in Sugar Handling

  • Fire and Explosion Hazards of Dried Sewage Sludge, by S. J. Manchester, published in 2001

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