U.S. Fire Administration/Technical Report Series

Special Report:

The Hazards Associated 

with Agricultural Silo Fires

USFA-TR-096/April 1998

U.S. Fire Administration Fire Investigations Program

T

he U.S. Fire Administration develops reports on selected major fires throughout the country. 

The fires usually involve multiple deaths or a large loss of property. But the primary criterion 

for deciding to do a report is whether it will result in significant “lessons learned.” In some 

cases these lessons bring to light new knowledge about fire--the effect of building construction or 

contents, human behavior in fire, etc. In other cases, the lessons are not new but are serious enough 

to highlight once again, with yet another fire tragedy report. In some cases, special reports are developed to discuss events, drills, or new technologies which are of interest to the fire service.

The reports are sent to fire magazines and are distributed at National and Regional fire meetings. The 

International Association of Fire Chiefs assists the USFA in disseminating the findings throughout the 

fire service. On a continuing basis the reports are available on request from the USFA; announcements of their availability are published widely in fire journals and newsletters.

This body of work provides detailed information on the nature of the fire problem for policymakers 

who must decide on allocations of resources between fire and other pressing problems, and within 

the fire service to improve codes and code enforcement, training, public fire education, building 

technology, and other related areas.

The Fire Administration, which has no regulatory authority, sends an experienced fire investigator 

into a community after a major incident only after having conferred with the local fire authorities 

to insure that the assistance and presence of the USFA would be supportive and would in no way 

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during the event or even immediately after, but rather after the dust settles, so that a complete and 

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For additional copies of this report write to the U.S. Fire Administration, 16825 South Seton Avenue, 

Emmitsburg, Maryland 21727. The report is available on the Administration’s Web site at http://

www.usfa.dhs.gov/

The Hazards Associate with

Agricultural Silo Fires

Authored by: Alan Clark

John Kimball

Hollis Stambaugh

This is Report 096 of the Major Fires Investigation Project conducted 

by Varley-Campbell and Associates, Inc./TriData Corporation under 

contract EME-94-C-4423 to the United States Fire Administration, 

Federal Emergency Management Agency.

Department of Homeland Security

United States Fire Administration

National Fire Data Center

U.S. Fire Administration

Mission Statement

As an entity of the Department of Homeland 

Security, the mission of the USFA is to reduce life and economic losses due to fire 

and related emergencies, through leadership, advocacy, coordination, and support. 

We serve the Nation independently, in coordination with other Federal agencies, 

and in partnership with fire protection and 

emergency service communities. With a 

commitment to excellence, we provide public education, training, technology, and data 

initiatives.

ACKNOWLEDGMENTS

The U.S. Fire Administration greatly appreciates the cooperation received from the following people 

and organizations during the preparation of this report:

Timothy G. Prather Agricultural Safety Specialist

University of Tennessee Agricultural and Biosystems

Engineering, Knoxville, TN 37901

Bruce Warren Director of Engineering

A.O. Smith Harvestore Products, Inc

DeKalb, IL 60115

Tom Aliek A.O. Smith Harvestore Products, Inc.

DeKalb, IL 60115

Mr. Ken Musser International Silo Association

Lafayette, IN

TAbLE OF CONTENTS

ACKNOWLEDGMENTS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . vii

INTRODUCTION. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

SCOPE OF THE PROBLEM. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

SILAGE PROCESS AND FIRE RISK. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

TYPES OF SILOS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

FIRE CAUSES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

CASE STUDIES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

Case Study 1. Explosion in Conventional Converted Oxygen-Limiting Silo, 

Louiston, Minnesota. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8

Case Study 2. Explosion in Oxygen-Limiting Silo, Moville, Iowa. . . . . . . . . . . . . . . . . . . . . . . 9

Case Study 3. Fire in Conventional Silo, Elgin, Minnesota. . . . . . . . . . . . . . . . . . . . . . . . . . . . 11

Case Study 4. Silo Fire Extended to Barn, Delmar, Iowa. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Case Study 5. Silo Fire and Explosion, Sawdust Storage, Statesville, North Carolina. . . . . . . . . 14

HAZARDS ASSOCIATED WITH SILO FIRES. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

1. Combustion Explosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

2. Grain Dust Explosion. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

3. Confined Space Dangers. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16

4. Toxic Gases. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

5. Electrical. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

6. Climbing/Falling. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

7. Chutes. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

8. Livestock. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18

9. Hoops or Bands. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

10. Structural Integrity. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

11. Exposure to Respiratory Toxins. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 19

PRE-INCIDENT PLANNING. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

FIRE SUPPRESSION OPERATIONS. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

Size-Up of Incident. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21

Staffing. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Equipment. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Tactics. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Oxygen-Limiting Silos. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

BIBLIOGRAPHY. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 26

1

Special Report:

The Hazards Associated With

Agricultural Silo Fires

April 1998

INTRODUCTION

Firefighting is by its very nature an occupation of considerable risk and potential danger. As a part of 

the United Stated Fire Administration’s Major Fire Investigation Project, this Special Technical Report 

has been produced to help inform firefighters of the particular danger of fires in agricultural silos 

and the hazards that may be encountered in fire operations in and around these structures. Silo fires 

and explosions have been responsible for the deaths and injuries of firefighters and civilians. Since 

1985, at least six firefighters have been killed in silo emergencies; three were killed in a silo fire 

explosion in Ohio, two in a different silo explosion in Georgia, and another was asphyxiated in a 

grain storage facility in Iowa. The lethal potential is also underscored by the fact that many civilian 

workers have lost their lives in non-fire situations in grain or silage storage facilities.

Some silo emergencies can be immediately life threatening and all can be dangerous to firefighters if 

appropriate safety precautions are not followed. This special report is meant to provide information 

to prepare for and safely extinguish fires in agricultural silos.

The most common purpose of a silo is to store and preserve foodstuff for livestock. Whether the 

product is ensiled corn, hay, or bermudagrass, adequate quantities of high quality feedstock is the 

basis of a profitable milk and livestock production. Silos allow the controlled and flexible harvesting, storage, and disbursement of high quality feedstock. Hence, silos are an essential component 

of farm operations.

The use of silage has actually grown in popularity in the past 50 years because it maximizes the yield 

of nutrients from available land, decreases the cost of feed, lowers harvest losses, and increases the 

quality of the foodstuff. The use of silage can make the difference between a profit and a loss. Even 

with the capital outlays required for equipment, the mechanization of harvesting and storage reduces 

labor costs and related requirements. A trend toward greater silage use is likely to continue as more 

dairy and livestock producers graduate to year-round feeding of storage feedstocks and as livestock 

operations increase in size. 

As with all emergency operations, no single guide can cover every possible scenario. Results vary 

with each situation. Experience and proven methods should be used in addition to guides in extinguishing silo fires. However, each silo fire needs to be analyzed and decisions made based on the 

specific factors of the individual fire. The information in this special report can assist fire officers 

in the strategic and tactical planning for agricultural silo fires. As in any fire size-up and decisionmaking process, the most important factor is personnel safety. 
2 U.S. Fire Administration/Technical Report Series

SCOPE OF THE PRObLEM

In today’s farm economy, the silo is an integral component of a feed management system. Silo fires, 

therefore, can be very costly to farmers. In large modern operations, the amount of silage required 

is carefully calculated based on the farmer’s cost per pound of meat or per gallon of milk produced. 

The interrelationship of yield of silage per acre, nutrient value per ton, required output of meat or 

milk, and cost per ton of silage could be upset by a catastrophic fire that destroys significant amounts 

of silage. Another concern for the farmer is the difficulty of obtaining silage from alternate sources 

if silage is destroyed. The cost is considerably more per ton since silage does not lend itself well for 

transfer and shipment over long distances or extended times. The loss of silo operations can portend 

serious financial trouble.

In some respects, silos can be considered the rural version of a highrise building. Similar challenges 

include the elevated area in relation to the rest of the farm buildings, limited access, and laborintensive operations requiring coordination of resources. Like highrise fires, however, silo fires 

can be managed with an organized and methodical approach, utilizing on-scene resources and the 

information gained in pre-incident planning. Silo fires can be life-threatening in addition to being 

resource intensive. The following incidents indicate the potential dangers of silo fires.

Marshallville, OH, August 27, 1985

Three firefighters were killed while they were attempting to extinguish a fire in an oxygen-limiting 

silo by spraying water into the silo. They were on the top of the silo directing a water stream when 

an explosion lifted the concrete roof of the silo approximately four feet in the air, throwing the firefighters to the ground and into the silo.

By directing water into the top of the silo from the roof, air was entrained from the hose stream 

into the area of incomplete combustion. This provided oxygen into an atmosphere of high heat and 

sufficient fuel, which then causes an explosive backdraft. 

Bostwick, Morgan County, GA, August 5,1993

Two firefighters were killed when they applied water and foam to a fire in an oxygen-limiting silo. 

The explosion blew the roof off, sending one firefighter to the ground over 100 yards away and the 

other through the roof of a nearby metal building. Two firefighters on the ground were injured by 

debris. The top 15 feet of the silo were severely damaged by the explosion and an adjacent silo was 

dented by the debris, attesting to the force of the blast.

SILAGE PROCESS AND FIRE RISK

In the process of storing silage a plant material, “forage,” is harvested and stored in a container, 

“silo,” where it is preserved for livestock use. Silage is a preserved forage that may consists of grain 

crops such as chopped corn or sorghum; or legumes such as alfalfa, bermudagrass, or other hay 

crops. A fermentation process develops in the silo that preserves the silage.

The forage is chopped into small pieces and stored at 45 to 70 percent moisture and packed tightly in 

the silos. The material must be packed in order to force air out of the mass of forage for the preserving process to work properly. As the still-living forage is stored, it continues to respire, consuming 

the oxygen in the ambient air. As the air is used up, anaerobic (without air) bacteria multiply and 
USFA-TR-096/April 1998 3

consume plant sugars to produce lactic acid which raises the acidity of the silage. This action kills 

the bacteria and halts the fermentation process. At this stage the silage is stable.

If oxygen becomes available from breaches in the silo structure, the aerobic bacteria growth begins 

again. This growth consumes oxygen, uses nutrients, and causes heating. The consequences of this 

range from loss of nutrients and less efficient feedstock to spontaneous heating sufficient to cause 

ignition. If the silage is too dry when stored, is allowed to dry out, or is not densely packed, and if 

the oxygen is available due to poor structural conditions, spontaneous ignition is possible. 

TYPES OF SILOS

In order to conduct fire planning for silos, fire departments must recognize the basic silo types as 

well as the construction features, identifying characteristics, and hazards associated with each type.

Silos are categorized generally as horizontal (bunker) or vertical (tower).

Horizontal Silos

Horizontal silos can be either an above-ground bunker, a trench, or a large stand-alone mound of silage 

contained in plastic. These trenches or above-ground bunker silos are generally used for large herds 

requiring 400 tons or more of silage. They are constructed by mounding the soil around a trench or 

by sinking concrete walls into a trench. These “structures,” present the hazards of below-grade and 

confined space operations and the production of silo gases. Spontaneous ignition also can occur.

Vertical Silos

Vertical or tower silos are upright structures ranging in height from 30 to 120 feet with the 60- to 

80-foot range being the most common. Silos may measure from 12 to 30 feet in diameter, though 

most are between 20 and 24 feet.

The two most important types of vertical silos are conventional and oxygen-limiting or “controlled 

atmosphere.” The differences are basic, but the ability to distinguish between the two can literally 

make the difference between life and death in the event of a fire. Diagram 1 illustrates the basic differences between the two types of silos.

Conventional--Conventional silos are by far the 

most common type of silo. They are massive 

structures. An average size (20’ x 60’) concrete 

stave silo can weigh 70 tons and hold seven times 

that weight in silage, depending on the product 

stored. These silos are built on a reinforced concrete pad or base. It is not unusual for several silos 

to be erected side-by-side servicing a command 

feed room. 

The most common conventional silo is one constructed of concrete staves. Staves are curved 

rectangular-shaped concrete blocks each weighing 70 pounds or more which are held in place 

by reinforcing bands made of high strength steel. Diagram 1. Types of Silos
4 U.S. Fire Administration/Technical Report Series

The bands are threaded on each end and bolted together to form a circle around the exterior of the 

staves. Conventional silos may also be constructed of wood, poured concrete, tile blocks, or steel.

Main Features--There are two main characteristics of conventional silos: an unloading chute that runs 

the vertical length of the exterior of the silo, and an open top or loosely constructed dome. The 

chute is about 3’ in diameter and is used to unload and drop silage into a conveyor belt or feed room. 

The unloading chute can be steel, sheet metal, or fiberglass. Unloading doors are located every few 

feet in a column configuration similar to a floor opening. The unloading doors, located inside the 

unloading chute, are most commonly wood with steel hinges, handles, and ladder rungs bolted 

through the door.

The dome or roof cap can be constructed of fiberglass, aluminized steel, or other similar materials. 

Those silos with a roof cap or dome generally have 

a fill tube and loading door on the side of the top 

of the dome. Many concrete stave silos have a metal 

fill platform at the top of the outside ladder. Many 

of the silos also have a steel safety cage surrounding 

the exterior ladder. Ladders and loading door platforms are all less frequently found on the block and 

wood silos. Conveyor belts many times are located 

directly below the unloading chute to transfer silage 

to feed bunks in nearby feedlots. (See Diagram 2.)

Oxygen-Limiting--One type of vertical silo is an 

“oxygen-limiting” or “controlled atmosphere” silo. 

The purpose and function of this type of silo is just 

as the name indicates: to limit oxygen as the silage is 

stored. While the conventional silo is constructed to 

minimize the free flow of air into the storage area, 

the oxygen-limiting silo is designed as solid construction to be nearly air-tight. They are commonly 

constructed of steel shells with an inner layer of 

glass bonded to the steel to protect it and augment 

the insulation properties. The outer covering may be a finish of a ceramic and enamel coating. Poured 

concrete and fiberglass silos also are in operation today. Conventional silos of poured concrete construction can be converted to function as oxygen-limiting silos. The danger here is that these silos 

appear to be conventional, but they are actually oxygen-limiting and must be treated as such. The 

primary characteristics will be no silo openings, no unloading chute, and a fill pipe extending into 

the top of the dome. Conversion will also be identified by the bottom-unloading configuration.

Main features--The primary identifying feature of oxygen-limiting silos is the absence of an unloading 

chute on the exterior of the silo. Common characteristics of oxygen-limiting silos can also include 

a fill door located in the center of the top of the silo roof, a roof hatch rather than a loading door, a 

center fill pipe attached to a blower or fill pipe, or a single unloading door at the bottom of the silo. 

Oxygen-limiting silos primarily use bottom unloading--filling from the top and removing silage 

from the bottom. Most oxygen-limiting silos also have a steel ladder and safety cage leading up to 

and across the roof to the center fill door. (See Diagrams 3 and 4.)

Diagram 2. Features of Conventional 

Vertical Silo
USFA-TR-096/April 1998 5

Other features that may be found on oxygen-limiting silos include two-way pressure relief valves on 

the roof, roof hatches, and access doors at ground level with safety interlocks.

Two-way pressure relief valves compensate for interior pressure changes caused by temperature 

variations. (Diagram 5.)

Diagram 3 and 4. Features of an oxygen-limiting silo

Diagram 5. Oxygen-limiting silos must “breath” to compensate for 

temperature and pressure changes

Oxygen-limiting silo may also be equipped with a “breather bag” arrangement designed to compensate for pressure changes in the interior of the silo. (See Diagram 6.)

Warnings or safety decals may be posted on oxygen-limiting silos. These are primarily intended 

for farm workers in a routine setting. Firefighters should consider fires or incidents in an oxygenlimiting silo as an imminently hazardous situation, which could result in death or serious injury.
6 U.S. Fire Administration/Technical Report Series

Diagram 6. “Breather Bag” system in oxygen-limited silo

Conversion silos--Conversion silos are those that were constructed originally as conventional type 

silos and have been modified to be oxygen-limiting. Modifications consist of reinforcing masonry 

blocks and joints to prevent any air exchange. Another conversion type is that which has been constructed using concrete or fiberglass, but that which is of such structural integrity as to control the 

atmosphere and, limit the oxygen in the silo. (Diagram 7.)

The same cautions and recommendations apply to conversion silos as to the oxygen-limiting silos: 

Do not attempt to enter, breach, or otherwise attempt to extinguish fire in a converted conventional to oxygen-limiting silo.

FIRE CAUSES

Different construction characteristics and contents 

of the two primary types of silos can result in different fire causes and personnel hazards. However, 

some of the universal causes are:

Spontaneous ignition-- The most common cause of 

fire in silos is spontaneous ignition. This usually occurs when the silage is stored at improper 

moisture levels or the silage particles are not properly sized. Care must be taken to ensure the proper 

moisture and distribution of silage. Silage contains 

living cells that continue to respire (breath) using 

oxygen-consuming plant sugars and producing 

heat. Generally, as the oxygen is consumed and 

the natural fermentation process slows, the silage 

reaches a stable state. This occurs approximately 

three weeks after storage in the silo. However, if 

the anaerobic process continues for a long period, 

the temperature of the contents can rise to the 

temperature necessary to produce spontaneous 

ignition. Documented cases of spontaneous ignition have been recorded in silage that has been Diagram 7. Conversion type of silo stored for over two years.
USFA-TR-096/April 1998 7

Fires are much less common in “oxygen-limiting” silos than in “conventional” silos, but the death 

and injury potential is much greater. That is because the former are designed to be airtight. If any of 

the latches or doors is left even partially open or the structural integrity is breached through leakage, 

air will enter the storage area and hasten the spontaneous combustion process. Toxic and explosive 

carbon monoxide is produced in much the same process and principle as a backdraft. If an ignition 

source is produced or the balance of the incomplete combustion is upset, an explosion is likely. These 

backdraft-like events have resulted in fire fighter fatalities as noted in the Incident Summary.

Lightning-- As silos are generally the tallest structures on the farm, they are prone to severe damage 

from lighting strikes. Lightning rod protection systems can prevent damage to the structure, but 

damage and fire can still result if lightning strikes hit the facility’s electrical system.

Mechanical heat of friction-- Loading or unloading belts, pulleys, shafts, and other mechanical apparatus 

are subject to mechanical failure and overheating.

Electrical-- New motors used in silos and feed rooms have safety devices; but many older electrical 

motors have been modified, and supporting wiring and circuitry may be substandard. Older or 

misapplied units such as these are prone to arcing and overheating.

CASE STUDIES

The following is a selection of sample incidents from 1991-1996 involving fires in silos. The case 

studies represent a range of silo-related fires and explosions. They illustrate the dangers and potential 

outcomes of silo fires, as follows:

1. A grain dust explosion in a converted oxygen-limiting silo.

2. A backdraft explosion in an oxygen-limiting silo.

3. A fire originating in a conventional silo that was successfully contained and extinguished.

4. A fire originating in a conventional silo that extended out of the silo, destroying several 

buildings.

5. A backdraft explosion in an oxygen-limiting silo in a nonagricultural setting.
8 U.S. Fire Administration/Technical Report Series

Case Study 1. Explosion in Conventional Converted 

Oxygen-Limiting Silo, Louiston, Minnesota

The Explosion

On Tuesday, October 15, 1996, at approximately 3:15 p.m., a silo explosion rocked a farm near 

Louiston, Minnesota. The explosion occurred on a sunny day with no thunderstorm activity. The 

owners were picking corn and placing it in a 21-feet-diameter by 30-feet-tall fiberglass oxygenlimiting silo. The corn blown into the silo was high moisture (24 percent) and was brought directly 

from the field to the silo. The silo was approximately 18 years old.

A person hired to fill the silo was directing the corn through a metal fill pipe into the top of the 

fiberglass silo. The top hatch had not been opened prior to ensiling the corn. According to a second 

hired man, the explosion occurred about two minutes after the filling process began. Eyewitnesses 

said the explosion shook dust off the rafters in the feed room next to the silo and was heard by others 

working in the farmyard.

Scene Examination

Examination revealed a large crack in the upper third of the fiberglass silo. The break was located in 

the vapor space above the corn which was stored in the bottom portion of the silo. 

In previous practice when the silo was being filled, the top hatch was left open to allow corn dust 

to escape the silo. This time the hatch was closed, promoting conditions favorable for a grain dust 

explosion:

•	 a supply of oxygen from air inside the silo;

•	 a fuel source (grain dust-corn dust) added in the filling process;

•	 dry grain dust suspended in the air; and

•	 proper ratio of dust to air located in a confined space.

The only thing missing was an ignition source.

Ignition Source

No electrical, heat-producing, or open flame devices were located or being operated at the top of the 

silo. No lightning storms were in the area at the time if the explosion. Based on the site investigation, the source of ignition was determined to have been a static spark generated by blowing corn 

through the undergrounded metal fill pipe of the silo.

Corn dust has the following characteristics according to section 5, chapter 9, of the 16th Edition of 

the Fire Protection Handbook published by NFPA.

•	 explosibility index 6.9 (Scale of 0-10+);

•	 explosion severity 3.0 (Scale of 0-2+); and

•	 maximum explosion pressure 113 PSIG.
USFA-TR-096/April 1998 9

The above characteristics of corn dust create the 

potential for a “severe” explosion. Eyewitnesses 

recalled hearing the explosion, then seeing the 

crack or break in the silo. Grain dust explosions 

can generate overpressures in excess of 100 PSI. 

For comparison, wood-framed walls can normally 

withstand pressures of 1-2 PSI, and concrete structures can withstand 2-8 PSI.

Conclusion

Grain dust explosions can occur within an oxygen-limiting silo. Firefighters must use caution if 

presenting conditions indicate the possibility of a 

dust explosion. Generally, oxygen-limiting silos 

prevent the conditions necessary for a dust explosion. However, if the balance is upset, a dust explosion can occur. The force generated by such an 

explosion is sufficient to damage heavy structural 

members and cause injury or death in a substantial surrounding area. Damage to silo from explosioncrack in 

vapor space

Case Study 2. Explosion in Oxygen-Limiting Silo, 

Moville, Iowa

The Explosion

On Tuesday, April 29, 1994, at approximately 9:30 a.m., an explosion occurred at a farm near Moville, 

Iowa, in an oxygen-limiting silo being used to store corn silage and haylage. The owners were 

attempting to unload the silo contents from the bottom in order to reach a level where silage had 

been burning slowly for over a week.

The explosion occurred at approximately 9:30 a.m. and ripped the roof off of the silo. Although 

workers were in or near the feed room, no injuries were reported.

Scene Examination

An investigation into the explosion revealed that the roof of the silo was blown off and landed about 

100 feet from the silo. Bolts were torn through the upper walls of the silo and the steel sheets were 

left crinkled in the upper portion of the structure. The breather bag was found to be broken. This 

breach in the bag was the source of air (oxygen) which allowed a spontaneous combustion fire to 

develop in the sealed storage unit.

The explosive gas in this incident was believed to be carbon monoxide (CO), which has an explosive 

range of 12.5 percent to 74 percent. The ignition temperature of carbon monoxide gas is approximately 1130 degrees Fahrenheit.
10 U.S. Fire Administration/Technical Report Series

Upon ignition, the pressure wave proceeded up the silo with enough force to explosively expel the 

roof. The resulting vacuum inside the silo crushed the side of the silo due to pressure differential 

created by the explosion.

Ignition Source

The spontaneous combustion fire within the haylage and corn silage produced a high enough temperature to ignite a concentration of carbon monoxide gas within the vapor space of the oxygenlimiting silo.

Conclusion

Explosions can occur in oxygen-limiting silos. The force generated by such an explosion is sufficient 

to damage heavy structural members, and propel heavy objects great distances. In this case, a damaged breather bag allowed oxygen into the sealed unit and spontaneous combustion occurred. The 

fire caused by the spontaneous combustion ignited the carbon monoxide mixture in the silo, causing 

the backdraft-like explosion. The explosion generated sufficient force to propel heavy objects over 

one hundred yards.

Deformity of silo shell due to explosion
USFA-TR-096/April 1998 11

Travel distance of silo roof due to explosion

Case Study 3. Fire in Conventional Silo, Elgin, Minnesota

The Fire

On March 10, 1995, a fire believed to have been caused by spontaneous combustion was reported by a farmer to the Elgin Volunteer 

Fire Department.

After determining that the fire was contained and not subject to 

spreading, members of the fire department met to plan their attack. 

After pre-planning session of one hour and a review of safety procedures, the Elgin Volunteer Fire Department then responded with 

one pumper, one tanker, and two equipment support trucks.

Fireground Size-Up

Upon arrival at the scene, fire was observed in two areas from 

the loading platform. One spot of open burning on the surface of 

the silage was observed directly below the loading door. A second 

location of open burning was observed in the area of the unloading doors and chute. In this area, fire had burned out a “U”- or 

“V”-shaped pattern around the unloading doors and had burned 

out several of the upper doors as well. Heavy ash residue and glowing embers could be seen in the area of the unloading chute doors. 

Diagram 8. Fire near 

unloading doors
12 U.S. Fire Administration/Technical Report Series

Moderate to heavy smoke filled the vapor space and dome area. The conventional concrete stave silo 

was more than 50 percent full of silage.

The unloading chute was clear of smoke and a positive up draft was noted with the loading door 

open at the top of the silo.

Fire Extinguishment

An inch-and-one-half line was advanced up the exterior of the silo to the loading door platform. A 

firefighter used the line to attack the visible burning in the surface area. A second inch-and-one-half 

line was advanced up the unloading chute with a silo fire probe attached. This enabled firefighters to 

attack the fire from inside the unloading chute, saving them from actually having to enter the silo.

Extinguishment commenced in the silo interior with knock-down of burning contents achieved by 

using the probing nozzle. The contents were then shoveled through the chute, falling to the base of 

the silo. The burning silage was doused with water and remaining fire was wet down. During probing activities inside the chute, heavy smoke, heat, and steam were produced inside the silo. This 

was quickly dispersed by the use of positive pressure ventilation in the unloading chute. After one 

hour, enough fire had been extinguished to reduce the temperature within the vapor space of silo to 

approximately ambient air temperature.

Silo Entry

Due to a large cavity of burned-out silage around the unloading doors, a six-foot fire department ladder was placed from the unloading door over the silage to the silo unloader. This ladder was secured 

to the unloading door opening and to the unloader. Firefighters entering the silo were wearing 

safety harnesses and secured to anchor points above. At this time, the atmosphere inside the silo was 

clear with little evidence of smoke or steam.

Using a temperature probe, surveillance was conducted in the area of the unloading doors and the 

exterior walls of the silo. Crews worked in 30-minute shifts. They were monitored by a safety officer 

who communicated via portable radio from his vantage point on the loading door platform. No 

smoke or fire could be found at the conclusion of the fire ground operation. However, it is believed 

that the fire was only 95-98 percent extinguished because, once the unloading process began, spots 

of fire were discovered and wet down.

By 9:00 p.m., no further fire could be found and the owner was advised he could begin unloading 

the silage to a level one door below the lowest area of fire. 

Conclusion

Fires in conventional silos can be safely extinguished. There is generally time to pre-plan fire 

ground operations in conventional silos. Positive pressure ventilation can be used with good effect. 

Firefighters should always anticipate hot spots and burning embers after the primary extinguishment 

has been completed.
USFA-TR-096/April 1998 13

Case Study 4. Silo Fire Extended to barn, Delmar, Iowa

The Fire

On May 20, 1991, at approximately 4:30 p.m., a fire was discovered by farm owners who were 

feeding cattle from the east silo. Responding firefighters discovered the first evidence of fire in the 

east silo feed room. The fire quickly spread to the 28 x 120-foot cattle shed directly to the south of 

the silos. A 16 x 88-foot feed bunk south of the cattle shed was severely damaged and an adjacent 

50 x 60-foot dairy barn located southeast of the cattle shed was totally destroyed by fire as well. The 

contents of one of two 18 x 88-foot concrete stave silos also was lost.

Ignition Source

Examination of the barn, feed bunk, cattle shed, and west silo failed to reveal any evidence of an 

ignition source for the fire. Examination of the east silo showed burn damage to the doors in the 

unloading chute to be more extensive on the inside of the silo than on the exterior surfaces of the 

wood doors. The fire’s origin was indicated to have been inside the silo.

Evidence discovered during the investigation was consistent with the initial cause declared as spontaneous combustion of the silage in the east silo. Hot embers dropping into the feed room during 

the unloading of the burning silage are believed to have spread the fire. These hot embers ignited 

combustible materials in the feed room. Fire then spread from the feed room to the cattle shed dairy 

barn and east silo. Silage in the west silo was found undamaged.

Conclusion

Spontaneous ignition in conventional silos can produce a slow developing fire which can be contained inside the silo if undisturbed. If the fire extends outside the silo, the blaze can move rapidly 

and cause extensive exposure fires.

Fire originated in the silo on the right, then extended to feed room dairy 

barn, cattle shed, and feed
14 U.S. Fire Administration/Technical Report Series

Destruction of farm buildings due to extension of spontaneous 

combustion-caused fire in silo

Case Study 5. Silo Fire and Explosion, Sawdust Storage, 

Statesville, North Carolina

The Fire

On December 21, 1997, at 8:35 a.m., fire units responded for a report of a fire in a silo to a facility 

that manufactured wooden reels for cord and cable. 

The silo in question was an oxygen-limiting silo of the type designed for storage of agricultural silage. 

It had been converted for use as a storage and transfer container for wood waste and by-products 

of the manufacturing process. Three fire companies responded and proceeded to apply water to the 

deep-seated fire in the silo. A crew was placed on the dome of the silo and operated a 1-3/4” attack 

line with a 30-degree fog pattern directed into hatch openings. After approximately two hours, the 

decision was made to remove access plates on the bottom of the silo and manually remove the wood 

products and complete the extinguishment of the fire. As the last bolt holding the plate was removed, 

both the crew on the top and the firefighters at the bottom of the silo noticed an inrush of air and a 

dull thump. This was followed by a loud, low-order explosion and fireball emanating from the area 

near the access hatch.

The Explosion

The explosion blew the roof structure and three firefighters from the top of the silo. One firefighter 

went straight up and landed in the interior of the silo, one was blown onto the top of a nearby shed, 

and the third was entangled between the top of the silo and the ladder cage from where he had been 

operating. Firefighters on the ground were propelled by the explosion away from the hatch opening, 

narrowly escaping injury. Moments before, the fire chief had removed personnel from the immediate 

vicinity of the opening.
USFA-TR-096/April 1998 15

A two-hour rescue operation was required to extricate the firefighters from inside and on top of the 

silo. The other firefighter was retrieved quickly from the shed. The firefighter who was dropped into 

the silo was hospitalized for second-degree burns to the face and neck. The one who was trapped on 

the top was treated and released for burns and contusions. The firefighter who landed on the shed 

suffered serious knee and shoulder injuries requiring surgery.

Conclusion

Explosions can occur in oxygen-limiting silos regardless of the products stored. Personnel 

should not be sent to the roof of an oxygen-limiting silo. Fire departments carefully evaluate 

the risk factors and consider defensive operations and exposure protection.

Damage to 

silo hatch at base; 

one firefighter blown 

onto the roof of shed 

at right.

One portion of 

the roof traveled 

approximately 400 

feet to the right.
16 U.S. Fire Administration/Technical Report Series

HAZARDS ASSOCIATED WITH SILO FIRES

The most serious and unique hazard of a silo fire is the explosion potential present in oxygen-limiting silos, but firefighters face other significant hazards in both types of silo configurations as well.

1. Combustion Explosion

As previously noted, oxygen-limiting silos pose a very real danger to firefighters from an explosion 

standpoint. Is a fire occurs in an oxygen-limiting silo from spontaneous combustion, carbon monoxide is produced and can collect in the vapor space of the silo. As the flammable range of carbon 

monoxide is very wide, from 12.5 to 74 percent, the potential for a backdraft-like explosion is very 

high. If exterior attempts to cool down the silo involve directing water through roof openings, air 

is drawn in from the outside, which may bring the flammable range concentration of CO into the 

right proportion for an explosion. The source of ignition is the heat of the spontaneous combustion 

that is already occurring. Any attempted entry into oxygen-limiting silos may cause rapid combustion explosion.

2. Grain Dust Explosion

Though normally not considered a silo fire hazard, grain dust in oxygen-limiting silos have been 

documented as the cause of some explosions. Case study number 2 is an example of this. If the 

dust inside the silo becomes suspended as result of fire operations and is ignited by the heat of a 

smoldering fire, a dust explosion can occur.

3. Confined Space Dangers

All silo entries should be treated as confined space entry because they fit all criteria of the definition. 

Firefighters need to be aware of the following possibilities:

•	 Toxic gases, depleted oxygen levels, and flammable gas mixtures may be present.

•	 Electrical energy, potential mechanical energy (such as hydraulic pressure), or energizable

machinery may endanger firefighters if such sources of energy are not controlled, locked out, 

and tagged out.

•	 Material may be “bridged.” Bridging occurs when the fire burns, creating a void in the silage

beneath what otherwise appears to be solid material. Bridging may also present as unevenly 

piled material, or appear as unstable ledges or overhangs of silage.

•	 Material may shift or be drawn to the bottom of the silo, causing anyone inside to be engulfed

and trapped in the silage. A firefighter may suffocate from this type of entrapment, even if 

wearing self-contained breathing apparatus.

•	 Vision may be obscured.

•	 Communication may be difficult.

•	 Small clearance areas may hamper mobility, especially while wearing breathing apparatus.
USFA-TR-096/April 1998 17

4. Toxic Gases

A number of hazardous atmospheric conditions are possible in silo incidents. Toxic gases may be 

produced by the reaction of the silage, incomplete combustion, or oxygen depletion. Among the 

specific gases are:

Nitrogen dioxide-- Exposure to nitrogen dioxide (NO2) can be fatal and is linked to a serious lung 

disease, commonly referred to as “silo filler’s disease.” (This is a term for chemical pneumonitis 

caused by exposure to nitrogen dioxide found in silage.) Nitrogen is produced when the oxygen is 

consumed in the fermentation process and the nitrates present in the plant material are released to 

form one of the oxides of nitrogen. As it escapes, it combines with the oxygen in the air to form the 

very toxic nitrogen dioxide. When NO2 is inhaled, it combines with the moist tissue of the respiratory system to form nitric acid. Strong concentrations of NO2 can create instantly lethal pulmonary 

edema due to the nitric acid in the lungs and throat. Reactions to moderate concentrations can cause 

pulmonary edema up to 30 hours later after the initial exposure, with the possibility of relapse in 

two to six weeks. The most dangerous period for encountering harmful nitrogen dioxide gas 

concentrations is from five to eight days after the silo is filled.

A particularly dangerous property of nitrogen dioxide is the synergistic affect with carbon dioxide 

which is also a byproduct of the silage process. At low level concentrations, nitrogen dioxide may 

cause little immediate pain or discomfort. The carbon dioxide present will cause an increase in respiration rates especially during a state of exertion (such as operating at a silo fire). This causes the 

individual exposed to inhale more rapidly and deeply, which brings the nitrogen dioxide deeper into 

the respiratory system without the warning of physical discomfort. If a firefighter inhales dangerous 

amounts of nitrogen dioxide, there is a high potential of developing fatal pulmonary edema, even 

well after the incident.

Nitrogen dioxide gas may be visible as a layered reddish/yellowish/brownish haze having a strong 

bleach-like odor. It is very toxic, having a Permissible Exposure Limit of five parts per million, and 

is heavier than air (vapor density is 1.58). Nitrogen dioxide gas may be present just above the top 

of the silage level and, being much heavier than air, may travel down the unloading chute and concentrate in low places such as the feed room, pits, or other below-grade areas. Other indicators of 

nitrogen dioxide gas are:

•	 strong burning sensation in the nose, chest, and throat;

•	 an acrid bleach-like odor;

•	 unnatural breathing of livestock;

•	 the presence of dead insects, animals or birds, especially in the lower levels of the silo/feed

rooms; and

•	 the presence of a yellow stain on silage, wood, or other materials.

Any of these warnings may indicate the presence of NO2 and extreme caution should be exercised. The use of self-contained breathing apparatus is indicated.
18 U.S. Fire Administration/Technical Report Series

Carbon dioxide-- Carbon dioxide gas is produced in quantity in the silage fermentation process. It is 

odorless, colorless, and tasteless, and heavier than air. Carbon dioxide is non-toxic, but displaces the 

air and lowers the oxygen level potentially to the point that respiratory distress can occur. Strong 

concentrations of CO2 can cause rapid asphyxiation due to oxygen insufficiency.

Carbon monoxide-- This gas is a product of incomplete combustion and is a potential hazard in oxygenlimiting silos. It is very toxic and causes asphyxiation by preventing oxygen from being carried in 

the red blood cells. It has a Permissible Exposure Limit of 50 parts per million and is lighter than air. 

The primary hazard of this gas in silo environments is, however, the threat of explosions due to the 

high combustibility of carbon monoxide.

5. Electrical

Firefighters face numerous electrical hazards in silo environments. Electrical cables run up the 

unloading chute to an electric motor attached to the unloader. Conveyors, feed systems, and lighting in the feed room all pose potential electrical hazards. Consequently, electric power should be 

controlled prior to entry of fire personnel, the application of water, or other fire operations.

Another electrical hazard is the presence of overhead wires or transformer poles. In the farm environment, these may be poorly marked, low to the ground, and in poor condition. Every year, an 

average of 62 U.S. farm workers are electrocuted in accidents.

6. Climbing/Falling

Many silos extend up to 100 feet in height, thereby presenting a climbing hazard. Although most 

silos have ladders with a safety cage, the condition of the ladder and supports should be examined 

before they are used. Firefighters should check the condition of the ladder and cage (rungs, side 

rails, nuts, bolts, rivets, and other fasteners) for signs of rust, missing pieces, age, and other signs of 

weakness or failure. They should avoid using the ladder if it is not in good condition.

Falling is a potential inside the unloading chute because silage, mud, water, or other debris can make 

for very slippery conditions. Unloading doors should be checked for secure closures and each hand 

hold or footstep should tested to ascertain structural soundness.

The entire operating area may be subject to mud, animal waste, and other debris.

7. Chutes

The condition of the chute itself should be observed in the conventional concrete stave silo. The 

chute is normally connected to the silo by the use of nuts and bolts. As with the exterior ladder and 

the doors, these should be checked to make sure they are secure and in good repair.

8. Livestock

Livestock penned in feed rooms, feed lots, and around the silo area should be removed prior to fire 

operations. If animals become frightened, they may be impossible to control during fire operations, 

presenting a safety hazard to themselves and firefighters.
USFA-TR-096/April 1998 19

9. Hoops or Bands

The hoops, bands, or rods binding the staves are structural components and should not be used as 

ladders, footholds, or handholds. They are not designed for such use and have sharp edges, connections, and other potential sources of injury.

10. Structural Integrity

The main structural members of the typical silo will be exposed (such as the hoops and bands). 

These and other structural members such as the staves should be monitored for signs of weakness 

due to fire, wind, rain, ice, or other environmental condition that may cause structural failure. 

Remember that the weight of the silo and its contents may exceed 70 tons. Load-related structural 

failure of silos may cause significant injury and extensive property damage.

11. Exposure to Respiratory Toxins

In addition to the hazards caused by the oxides of nitrogen and oxygen depletion, a number of other 

silage-related respiratory hazards exist for emergency responders.

Pesticide exposure-- Silage may contain the residue of various chemical treatments, which include pesticides and hay preservatives. Usually the pesticides are no longer present by the time silage is harvested 

and stored. However, the possibility of such exposure cannot be ruled out. If emergency personnel 

exhibit classic symptoms of pesticides poisoning (such as uncontrolled salivation and lachrymation, 

seizures, and other unexplained symptoms suggesting central nervous system damage), pesticide 

exposure may indicated.

Reaction to microorganisms--- Tiny spores which grow in wet silage appear as white dust. This dust 

is actually a mold-like bacteria called thermophilic actinomycetes. Hypersensitive reaction to this 

bacteria is called “Farmer’s Lung.” Four to eight hours after exposure to the “dust,” the individual 

exposed may develop flu-like symptoms (harsh cough, fever, chills, sweating, weakness, and shortness of breath). Farmers may build up a resistance to this bacteria. Those who are rarely exposed 

to this bacteria, such as emergency responders, may experience a sensitive reaction, resulting in an 

illness much like pneumonia. The term for this condition is hypersensitive pneumonitis.

Pulmonary mycotoxicosis--- This condition is closely related to hypersensitivity pneumonitis, but is not 

associated with dust clouds of mold spores. This is caused by a fungus that develops in the top layer 

of exposed silage and causes a toxic reaction in the lungs. The symptoms are: burning in the eyes, 

throat, and chest; chills; fever; headache; and a dry, irritating cough.

Organic Toxic Dust Syndrome--- Another respiratory illness, which may result from exposure to silage 

contaminated with microorganisms, is Organic Toxic Dust Syndrome (ODTS). This syndrome is 

characterized by fever and flu-like symptoms, shortness of breath, and impaired pulmonary function. An increase in white blood cell count may also be a sign of ODTS. It is commonly misdiagnosed 

as farmer’s lung disease.
20 U.S. Fire Administration/Technical Report Series

Two important cautions should be remembered about exposure to respiratory toxins:

•	 Exposure to respiratory toxins can be prevented; always wear self-contained breathing

apparatus in these atmospheres.

•	 In the event respiratory protection is not afforded, be very specific about information

provided to medical personnel as to the symptoms and means of exposure.

PRE-INCIDENT PLANNING

Pre-incident planning can provide critical information needed to safely and effectively combat silo 

fires. A fire department can and should identify the types and locations of silos in their response 

area and maintain such information at their station, communications center, and on the command 

vehicle.

The types of information needed are:

•	 contact information (telephone, pagers) for silo manufacturers, dealers, or others with specialized technical knowledge who will provide assistance during emergencies;

•	 location and types (conventional, oxygen-limiting, conversion);

•	 size of silo; dimensions and capacity;

•	 type(s) of silage generally stored;

•	 vehicular accessibility to silo;

•	 identification and protection of exposures; and

•	 water sources.

This information should be reviewed and updated periodically. It can be used for training and should 

be readily accessible response information.

FIRE SUPPRESSION OPERATIONS

As with any fire operation, firefighters should carefully evaluate the hazard and risk factors in silo 

fires. The fires are generally contained and may present no immediate danger. This is especially true 

of conventional silos. The proper risk assessment of the oxygen-limiting silo is: Do not attempt to 

enter, breach, or otherwise attempt to extinguish fire in oxygen-limiting silos. There is nothing 

to gain and firefighters’ lives are at considerable risk. Call the manufacturer’s representative and 

protect exposures.

Fires in conventional silos are slow burning, and, with the exception of embers falling down the 

unloading chute, are generally contained within the body of the silo. Fire departments can take the 

time not normally associated with more common types of fires to plan their response.

Firefighters should carefully consider the hazards, risks, and strategic objectives of silo fire operations. In determining the best tactical approach, these factors should be carefully considered:

•	 Life safety: always the primary factor. At most silo fires, the only lives in danger are those of

the responders.

•	 Fire conditions: deep-seated, slow-burning, or rapidly developing, free-burning.
USFA-TR-096/April 1998 21

Exposures: distance, construction.

•	 Weather conditions: winds, humidity, electrical storms.

•	 Property: firefighters may prioritize the property to be protected in relation to proximity,

value, and function.

•	 Protection of livestock: location and number.

•	 Resources: sufficient numbers of trained personnel and proper type and amount of

equipment.

•	 Water supply: availability of sustained water supply, ability to deliver to the scene and apply

to fire.

•	 Electrical services: transformers, wires, and disconnects.

The first step in planning the attack is to review the information acquired during the pre- incident 

planning phase. If this has not been done in advance, time must be taken at the incident to review 

the vital information and consider the age, type, and amount of silage loaded; weather conditions; 

time of day; and other incident-specific variables.

Some departments meet at the fire station to develop a plan of attack after acquiring the above information. This gives them an opportunity to review safety plans, incident command structure, equipment needs, staffing needs, and assign specific duties to responding fire fighters. (Some departments 

actually conduct a safety review prior to going to the scene for suppression operations.)

Size-Up of Incident

The extent and location of the fire can 

possibly be determined from the exterior 

of the silo as the following photograph 

indicates. The dry area around the unloading chute and below the loading door is 

an indication of fire. Outside observation 

can quickly indicate the dry area where 

the heat of the fire has dried the concrete 

staves. This pinpoints the location of the 

heaviest fire involvement. Size up may 

include observation of the interior via 

the outside ladder to the loading door 

platform.

Fire and smoke conditions must be carefully observed. Smoke may be issuing 

from the doors, chutes, or the dome area. 

The volume and force of the smoke as it 

exits the silo will be a good indication of 

the extent of fire within the silo.

Usually fire will occur in the top ten feet 

of silage, but it can and will burn deeper 

Color differences indicate area dried due to 

heat of fire
22 U.S. Fire Administration/Technical Report Series

around the unloading doors. To assist with ventilation of the silo, open as many doors as possible 

above the top of the silage.

For operations on and in the silo interior, this should be completed with the team entry and back-up 

procedure. Full turnout gear and SCBA should be standard personal protective equipment. Incident 

commanders may elect to make a limited visual survey of the interior to assess conditions.

Prior to initiating the entry and beginning the extinguishment phase, all command personnel, support staffing, and necessary equipment should be assembled. An essential decision process at this 

point is an assessment of hazard and risk. The incident commander must make a decision based on 

the stability of the structure, the extent of the fire, the availability of personnel and equipment, and 

the exposures involved.

In some cases, the fire may have left little or no salvageable foodstuffs and the condition of the silo 

may preclude entry for firefighting. A proper course of action may be to close all exterior openings 

and allow the fire to burn out. This can take a period of several weeks, and should be regularly monitored for flare-ups or exposure fires.

Staffing

One of the primary strategic and tactical considerations is staffing. Sufficient personnel should be 

available to support an operation that includes:

•	 Command:

The Incident Commander should establish a command post at a safe vantage point to permit 

effective observation of the scene. The incident commander should remain visible to implement the command system and permit coordination of resources.

•	 Safety/Observer:

The Incident Commander should designate a Safety Officer as early in the incident as possible. In silo fires, the Safety Officer should pay particular attention to the climbing and entry 

procedures, use of full protective clothing including SCBA, and the timing and accountability 

of firefighters working in the silo. The Safety Officer should also be sensitive to the requirements of rotating the firefighters in strenuous assignments.

•	 Entry:

A sufficient number of firefighters to do the hands-on extinguishing and overhaul should 

be organized under an “Entry” or “Interior” sector officer. At least two firefighters should 

perform operations as a team inside the silo.

•	 Back-Up:

A back-up or rapid intervention team of at least two fully equipped firefighters should be in 

close and constant visual or verbal contact with the entry crew. A good arrangement places 

an observer at the top of the silo who can observe and communicate with the entry team as 

well as alerting the back-up team to initiate support if needed.

•	 Water Supply:

The Incident Commander should organize water supply operation to support a steady and 

uninterrupted flow of water for attack and overhaul. A sufficient reserve for emergency withdrawal coverage should be maintained as well.
USFA-TR-096/April 1998 23

All personnel should be accounted for at all times. Personnel must be rotated regularly if the decision 

is made to enter the silo, unload the contents, and extinguish the fire. This work is fatiguing and provisions should be made for crew relief and rehabilitation as well as for fluid replacement and food.

Water is the preferred extinguishing agent. Foam, whether it is protein-base, aqueous film forming 

foam, or flouroprotein is generally of little value in silage fires. The penetrating and cooling properties of plain water are superior to foam and most covering agents in silage fires.

Equipment

•	 Full turnout gear with self-contained breathing apparatus is required to operate in silos and

chutes. Supplied air (airline respirator) can also be used by attack crews operating in the silo 

itself if such equipment is available.

•	 Firefighters in the silo should

be equipped with safety harness 

and anchored to secure points via 

approved safety lines. 

•	 A probing or piercing nozzle is

useful. It must be of sufficient 

size and construction to penetrate 

four to six feet into silage for 

direct water application of at least 

100 gallons per minute (gpm). 

Multi-directional nozzles such as 

a pierced-piping appliance can be 

used to great advantage to bore into 

the silage and apply water to the 

seat of the fire.

•	 Temperature probes, varying from

two to six feet in length, can help 

pinpoint the location and extent of 

the burn area in silage layers.

•	 Lighting equipment should be

used for exterior illumination and 

for interior operations.

•	 Ventilation fans may be employed

for positive pressure ventilation.

•	 Sufficient radios and batteries

will be required for extended 

operations.

•	 Auxiliary power will be required

for light and ventilation. Diagram 9. Temperature Probe
24 U.S. Fire Administration/Technical Report Series

Tactics

When the decision is made to attack and extinguish 

the fire, the logical progression of knocking down visible exterior fire at the base should be the first priority. 

Positive pressure ventilation (PPV) should be applied 

at the base of the silo to clear heat, smoke, and gases 

from the fire area. PPV has been used to great advantage in these situations. However, firefighters must 

be alert for ashes or embers as well as increased fire 

intensity once PPV is utilized. Charged, supplied hose 

lines should be standing by before PPV is applied.

As crews enter the silo for extinguishment, great caution must be exercised. The burning silage may have 

created holes underneath that may not be visible. For 

this reason, entry crews should be tied off by a safety 

harness and line, and properly anchored. Ladders 

or other secure platforms can be used to distribute 

weight, but bridging of the contents can present very 

unstable situations.

The use of a temperature probe and penetrating nozzle may be used to good advantage. Probing should 

be done along both sides of the doors and around the periphery and near any other pockets exhibiting 

smoke or heat. The most common fire situations are noted in Diagram 10. These are typical fire patterns 

around the doors and the diameter of the silo. In some 

fires, both of these patterns will develop with burning 

around the exterior and fire also extending along both 

sides of the unloading doors in a “U”- or “V”-shaped 

pattern. Usually the hot spots in the silage can be easily identified through the resistance encountered by 

probes or by the reading from the temperature probes. 

Any area exceeding 180 degrees Fahrenheit should be 

injected with water.

Care must be taken if a flooding tactic is utilized. The 

bum pattern may extend from the ground up to the 

entire vertical length of the silo, creating an eccentric 

and unbalanced content load. As water is injected into 

the silage, it is absorbed and the dynamic weight of 

the load is greatly increased. In most silos, the content 

weight is designed to be transferred to the ground. 

Additional water loading increases the lateral load in 

an area that has little designed structural strength for 

lateral loading.

Diagram 11 depicts a firefighter using a probe to 

determine the location and extent of fire in the silo 

contents.

Diagram 10. The most common fire 

situation in conventional silos

Diagram 11. Probing for hot spots in silage
USFA-TR-096/April 1998 25

OxYGEN-LIMITING SILOS

Under no circumstances should firefighters attempt to extinguish fires in oxygen-limiting silos. 

Rather, they should contact the manufacturer’s representative or dealer. Extinguishment may be 

accomplished by injecting nitrogen or carbon dioxide into the silo using special fittings and piping available from the dealer. Firefighters must consider oxygen-limiting silo fires as a probable 

backdraft risk. Backdrafts in oxygen-limited silos have explosive force that can blast heavy structural 

components hundreds of feet away.

Cautions for fire in oxygen-limiting silos are:

•	 Do not add water or foam to the structure.

•	 Stay off these structures if smoke or steam is observed coming out of the roof openings

(such as breather bag vents or pressure relief valves) and/or if rumbling and vibration of the 

structure is evident.

•	 Do not spray water into the structure or through any opening. Water will not penetrate 

or reach the burning material, but may draw air containing oxygen, which would cause a 

backdraft-like explosion.

•	 Do not spray water onto the structure as this will damage the structure itself and possibly 

cause an explosion. The water will not cool the structure, but will draw in air that could 

initiate an explosion.

•	 Assure that all unloaded doors, structure access doors, or any other openings are closed. If 

the structure is rumbling and vibrating, no approach should be made. The fire should be 

allowed to burn itself out. 
26

B

Thomas J. Maloney. “Combating Agricultural Silo Fires.” Speaking of Fire, International Fire Service 

Training Association. Oklahoma State University. Stillwater, OK: Oct. 1997.

Silo Operators Manual. International Silo Association. P.O. Box 560, Lafayette, Indiana 47902.

Extinguishing Silo Fires. publication #NRAES-18. Northeast Regional Agriculture Engineering 

Service. Cooperative Extension. 152 Riley-Robb Hall, Ithaca, NY 14853-5701.

Ted Halpin, Doug Shattuck. “Agricultural Silo Fires.” Fire Chief Magazine. H. Marvin Gin Corporation. 

Chicago, Illinois: September 1987.

“NIOSH Warns Farmers of Deadly Risk of Grain Suffocation.” Publication 93-116. April 1993. 

National Institute of Occupational Safety and Health, Department of Health and Human Services. 

200 Independence Avenue, SW, Washington DC, 20201.

“Preventing Fatalities Due to Fires and Explosions in Oxygen Limiting Silos.” Publication #86-118. 

June 1986. National Institute of Occupational Safety and Health, Department of Health and Human 

Services. 200 Independence Avenue, SW, Washington DC, 20201.

Dennis J. Murphy, “Silo Gases-the Hidden Danger.” Pennsylvania State University Fact Sheet #16. 1991. 

Pennsylvania Cooperative Extension Service, Pennsylvania State University, College of Agricultural 

Science, Agricultural Engineering Department. 246 Agricultural Engineering Building, University 

Park, PA, 16802.

Timothy G. Prather. “Silo Fires-Costly, Frustrating and Even Deadly.” news release. August, 1993. 

University of Tennessee Agricultural Extension Service. Knoxville, Tennessee 37901.

Bradley K. Rein. “Farm Safety: Prevention, Rescue, and Rehabilitation.” Document #0- 866-3 10. 

Farm Safety Fact Sheet. May 1991. United States Department of Agriculture Extension Service, 

Washington DC 20250-2260.

Charles V. Schwab, Laura Miller. “Electrocution Hazards on the Farm.” Fact Sheet Pm-1265k. Safe 

Farm Program. November 1992. Iowa State University Extension, Ames, Iowa.

“Agricultural Dusts and Gases.” Farm Occupational Safety Safety Information sheet. 1992. published 

by National Agricultural Library, United States Department of Agriculture. College Park, MD, 20850.