TR-096, The Hazards Associated with Agricultural Silo Fires*
The Hazards Associated with Agricultural Silo Fires 

SPECIAL REPORT 

United States Fire Administration 
Federal Emergency Management Agency 

United States Fire Administration 
Technical Report Series 

United States Fire Administration 
Major Fire Investigation Program 

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The Hazards Associated with Agricultural Silo Fires 

August 1998 

SPECIAL REPORT 

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 EMW-94-C-4423 
to the United States Fire Administration, Federal Emergency Management Agency. 

United States Fire Administration 
Federal Emergency Management Agency 

TABLE OF CONTENTS 

ACKNOWLEDGMENTS................... 1 
INTRODUCTION............................... 2 
SCOPE OF THE PROBLEM.......... 4 
SILAGE PROCESS AND FIRE RISK... 6 
TYPES OF SILOS ...................... 7 
Horizontal Silos.............. 7 
Vertical Silos ........................ 7 
FIRE CAUSES ................................ 13 
CASE STUDIES............ 15 
HAZARDS ASSOCIATED WITH SILO FIRES............... 29 
COMBUSTION EXPLOSION .................. 29 
GRAIN DUST EXPLOSION.................... 29 
CONFINED SPACE DANGERS .............. 29 
TOXIC GASES .................................... 30 
ELECTRICAL.................................... 31 
CLIMBING/ FALLING.......................... 32 
CHUTES ........................................... 32 
LIVESTOCK ...................................... 32 
HOOPS OR BANDS............................. 32 
STRUCTURAL INTEGRITY ................. 32 
EXPOSURE TO RESPIRATORY TOXINS....... 33 
PRE-INCIDENT PLANNING.......... 34 
FIRE SUPPRESSION OPERATIONS..... 35 
SIZE-UP OF INCIDENT....................... 36 
STAFFING.......................................... 37 
EQUIPMENT .................................. 39 
TACTICS ......... 41 
OXYGEN-LIMITING SILOS .................. 43 
BIBLIOGRAPHY............................. 44 

1 

ACKNOWLEDGMENTS 

The United States Fire Administration appreciates the help of the following 
persons who reviewed 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 Engineered Storage Products Company 
DeKalb, IL 60115 

Tom Aellig A. O. Smith Engineered Storage Products Company 
345 Harvestore Drive 
DeKalb, IL 60115 

Drew Freeman President 
International Silo Association 
Lafayette, IN 47902 

Diagrams 3, 4, 5, and 6 from Silo Operators Manual, were used with permission 
from International Silo Association. 

Diagrams 1, 2, 8, 9, 10, and 11 from Extinguishing Silo Fires, publication 
#NRAES-18, were used with permission from Northeast Regional Agriculture 
Engineering Service, Cooperative Extension. 

2 

INTRODUCTION 

Firefighting is by its very nature an occupation of considerable risk and 
potential danger. As a part of the United States Fire Administration's Major 
Fires Investigation Project, this special 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.

3 

As with all emergency operations, no single guide can cover every possible 
scenario. Results vary with each situation. 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 
decision-making process, the most important factor is personnel safety.

4 

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 high-rise 
building. Similar challenges include the elevated area in relation to the rest 
of the farm buildings, limited access, and labor-intensive operations requiring 
coordination of resources. Like high-rise 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 caused an 
explosive backdraft.

5 

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.

6 

SILAGE PROCESS AND FIRE RISK 

In the process of storing silage a plant material, "forage", is harvested and 
stored in a container, "silo", in where it is preserved for livestock use. 
Silage is a preserved forage that may consist 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 percent 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 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 oxygen is available due to poor structural conditions, spontaneous 
ignition is possible.

7 

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.

Diagram 1. Types of Silos 

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.

8 

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 common 
feed room.

The most common conventional silo is one constructed of concrete staves. Staves 
are rectangular concrete blocks each weighing 70 pounds or more which are joined 
at angles and held in place by reinforcing bands made of high strength steel. 
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).

Diagram 2. Features of Conventional Vertical Silo 

9 

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 types will also be identified by 
the bottom-unloading configuration.

Conversely, steel shell oxygen-limiting silos can be converted to conventional 
silo operations. These units have significant structural integrity and retain a 
high potential for explosions. They can develop considerable burning void areas 
in the product with little outward evidence of fire. Explosive backdraft 
conditions are present in these voids. (Case Study #5)

An oxygen limiting silo that has been converted to a conventional silo should be 
subject to the same cautions as an oxygen-limiting silo. 

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).

10 

Diagrams 3 and 4. Features of an oxygen-limiting silo 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 5. Oxygen-limiting silos must "breath" to compensate for temperature and 
pressure changes

11 

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.) 

Diagram 6. "Breather Bag" system in oxygen-limited silo 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 oxygen-limiting silo as an imminently hazardous situation, which 
could result in death or serious injury.

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.)

12 

Diagram 7. Conversion-Type of Silo The same cautions and recommendation 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.

13 

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 stored for over 
two years.

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.

14 

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 mis-applied units such as these are prone 
to arcing and overheating.

15 

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 non-agricultural 
setting. 

Case Study Number One 
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 oxygen-limiting 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.

16 

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. 

Previously, 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 
 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 of 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 
ungrounded 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. 

 Explosiblity index 6.9 (Scale of 0-10+) 
 Explosion severity 3.0 (Scale of 0-2+) 
 Maximum explosion pressure 113 PSIG 

17 

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.

Damage to silo from explosion crack in vapor space 

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.

18 

Case Study Number Two 
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 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 a 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.

Upon ignition, the pressure wave proceeded up the silo with enough force to 
explosively expel the silo 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 oxygen-limiting silo.

19 

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 

20 
Travel distance of silo roof due to explosion 

21 

Case Study Number Three 
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 a 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. 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.

Diagram 8. Fire near unloading doors 

22 

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.

23 

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.

24 

Case Study Number Four 
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' cattle shed directly to the south of the silos. 
A 16' x 88' feed bunk south of the cattle shed was severely damaged and an 
adjacent 50' x 60' dairy barn located southeast of the cattle shed was totally 
destroyed by fire as well. The contents of one of two 18' x 88' 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.

25 

Fire originated in silo on right, extend to feed room dairy barn, cattle shed 
and feed 

Destruction of farm buildings due to extension of spontaneous combustion -caused 
fire in silo 

26 

Case Study Number Five 
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 
botton 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.

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.

27 

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 roof of shed at right 

28 
One portion of the roof traveled approximately 400' to the right 

29 

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.

Combustion explosion 

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

Grain dust explosion 

Though normally not considered a silo fire hazard, grain dust in oxygen-limiting 
silos has been documented as the cause of some explosions. Case study #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.

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 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. 

30 

 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. 

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.

31 

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 
 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.

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 oxygen-limiting 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.

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.

32 

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.

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.

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.

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.

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.

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

33 

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.

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 be 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.

34 

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 
 Water sources 

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

35 

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 
 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:

36 

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.

Color differences indicates area dried due to heat of fire 

37 

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 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.

38 

 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.

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.

39 

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. 

40 

Diagram 9. Temperature Probe 

 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. 

41 

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.

Diagram 10. The most common fire situation in conventional silos 

42 

Care must be taken if a flooding tactic is utilized. The burn 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 11. Probing for hot spots in silage 

43 

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 back draft 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 could 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. 

44 

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