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Timothy
G. Prather
University of Tennessee Extension
This
manual was prepared to inform Tennessee farmers and firefighters
about the causes, prevention and control of hay fires. The
information contained herein is believed to be accurate and
up-to-date. However, the University of Tennessee Agricultural
Extension Service will not be responsible for accidents, injuries
or any other losses resulting from the application of practices
described in this publication.
Fires that damage or destroy hay and barns cost farmers thousands of dollars in terms of building replacement, feed replacement and lost revenues. This is unfortunate, because proper harvesting and storage practices can practically eliminate hay fires.
What
Causes Hay Fires?
Hay fires usually occur within six weeks of baling, but they may occur in hay several years old. Fire can occur in loose hay, small bales, large bales or in stacks. The fires can occur in hay stored inside as well as in hay stored outside. Regardless of when or where the fires occur, the most common cause is excessive moisture.
Freshly
cut forage materials are not dead. Some respiration continues
and a very small amount of heat is produced. This heat generated
by respiration is probably of little consequence except that
it may help provide proper conditions for growth of bacteria.
As the moisture content of the crop decreases during the curing
process, respiration will slow and eventually cease.
Forage
crops are always contaminated with countless microorganisms.
These microorganisms are no problem when the hay is harvested
and cured to the proper moisture content before baling and
storage. After baling, however, a small supply of air and
a favorable moisture level cause the microorganisms to begin
to feed and multiply, generating heat in the process. This
heating continues up to a temperature of 130 to 140°F,
at which the heat tends to kill the microorganisms.
Depending
upon the exact conditions, the temperature may decrease slowly
at this point as the microorganisms are killed. The hay may
go through several similar heating cycles during the next
weeks as the population of microorganisms increases and decreases,
but the highest temperature will usually be lower each time.
Eventually the temperature will stabilize near the ambient
temperature.
Table
1. Hay Recommended Moisture Contents for Baling Hay |
Baling
Method |
Hay
Moisture Content1 |
Large
packages (round bale, stack) |
15-18% |
Conventional
square bale |
20-25% |
Using
innoculant based preservative2/3 |
20-25% |
Using
acid based preservative |
20-30%
|
1
- Maximum moisture contents are for grass and legume hays.
2 - Consult label recommendations and your Extension agent
before using preservatives or drying agents.
3 - As a general rule, the University of Tennessee Agricultural
Extension Service does not recommend the use of innoculant
based preservatives.
Source: Department of Plant and Soil Science : University
of Tennessee : Agricultural Extension Service |
No fire
results in a case like the one described above, but there may
be considerable heat damage to the hay. In some cases cows may
actually prefer the taste of the brown, heat-damaged hay but
the feed has decreased considerably in nutritional value.
Refer
to the point where the temperature reached about 130°F.
If there had been some thermophilic (heat loving) bacteria
present and the heat had been retained, a second heating phase
could have begun. This heating could generate enough heat
to raise the temperature as high as 160 to 170°F before
bacterial activity ceases.
The
thermophilic bacteria and the heat they generate convert the
hay to a form similar to a carbon sponge with microscopic
pores. In this form and at the high temperatures present in
heated hay, the material combines readily with oxygen. It
can self-ignite in the presence of air and its tendency to
burn is almost unbelievable.
Preventing
Hay Fires
Since the moisture content of hay is a key factor in microbial activity and the resultant heating, it is important that the crop be cured to the proper moisture content before baling. Maximum moisture contents recommended by the University of Tennessee Agricultural Extension Service are listed in Table 1.
Weather
conditions greatly influence the rate at which the crops dry.
Ideal hay curing weather has less than 50 percent relative
humidity and some wind. Be aware that the moisture content
of the hay will increase overnight when the air is humid,
especially if there is dew or fog. Monitor weather forecasts
carefully to help schedule haymaking operations.
Conditioning
equipment which crimps or abrades the crop stems is helpful
because it speeds the drying process. Using tedders or hay
rakes to very gently fluff windrows may also speed the curing
process.
Chemicals
such as drying agents and preservatives, when properly used,
may be advantageous with some crops, such as high quality
alfalfa. Correct application is essential to avoid potential
problems.
New
hay which is stacked in the field or placed in a barn should
be checked frequently for possible heating. At first, check
in the morning and afternoon. If no signs of abnormal heating
are found, the intervals may be lengthened. If the temperature
reaches 130°F, move the hay to allow increased air circulation
and cooling.
Hay which is to be stored uncovered outdoors (big round bales
and stacks) should be formed into the tightest packages possible
to resist penetration by rain. Do not place unprotected bales
or stacks tightly against each other. Instead, place the bales
where air can circulate freely. Protect the bales from ground
moisture and runoff by placing them on a bed of gravel, old
tires, poles or pallets. Plastic or other waterproof covers
will protect bales by shedding precipitation.
If storing
hay inside, be sure the barn roof and any plumbing do not
leak. Likewise, provide adequate drainage so water will not
enter the barn during storms. Hay may be at the proper moisture
content when baled and stored, but wetting from a leak can
allow bacterial activity to increase and result in a fire.
There
are, of course, causes of hay fires other than spontaneous
ignition. Some of these causes are lightning striking nearby
trees or fences, arson, contact with electric fences and sparks
from cigarettes, welding or nearby fires.
Measuring
Hay Temperatures with a Probe
To accurately determine how hot it is inside a stack of hay you should use a probe and thermometer (Figure 1). The probe is pushed or driven into the stack and the thermometer is lowered to the end of the probe on a light wire. If the probe is horizontal, use a heavier wire to push the thermometer into the probe. After 10 to 15 minutes, retrieve the thermometer and read the temperature.
Table
2. Temperature Interpretations |
Below
130°F |
No
problem |
130
to 140°F |
No
problem yet, temperature may go up or down. Recheck in
a few hours. |
150°F |
Temperature
will most likely continue to climb. Move the hay to provide
air circulation and cooling. Monitor temperature often. |
175-190°F |
Fire
is imminent or may be present a short distance from the
probe. Call the fire department. Continue probing and
monitoring the temperature. |
200°F
or above |
Fire
is present at or near the probe. Call the fire department.
Inject water to cool hotspots before moving hay. Have
a charged hose ready to control blazing when moving hay. |
To check
the temperature without a probe and thermometer, push or drive
a 3/8 to « inch diameter metal rod into the hay and leave it
10 to 15 minutes. Pull the rod out and test its temperature
with your bare hand. If you can hold the rod in your hand comfortably
the temperature is below 130°F. If you can hold it, but
it is uncomfortable, the temperature is in the 130 to 160°F
range. If the rod is just too hot to hold in your bare hand,
the temperature is over 160°F and a fire is imminent or
nearby. Table 2 gives a list of temperature interpretations.
Several
probes and thermometers or several rods can be used at the
same time in various locations through the stack of hay to
complete the survey in a shorter period of time.
CAUTION:
If you see or smell smoke coming from the hay, place boards
or plywood on the hay before walking on top of it. This will
spread your weight over a larger area to prevent falling into
burned out cavities. A lifeline is also recommended in this
case.
Controlling
A Hay Fire
If you detect temperatures above 175°F, a fire is imminent or one is nearby. The smell or sight of smoke means a fire is definitely present. In any of these cases, call the fire department immediately.
Do not
move any of the hay. This would expose the overheated or smoldering
hay to oxygen and may result in a fire raging out of control.
The proper procedure for controlling a hay fire is as follows:
- Knock
down any visible flames. A straight tip nozzle will result
in deeper penetration.
- Probe
for hot spots and inject water through the probe to cool
the material and raise it to a moisture content that will
prevent burning.
- Remove
the hay to a safe location.
The
firefighter operating the probe should wear full turnout gear,
lifeline and a SCBA. Steam may blow back along the probe or
through other openings when water reaches a fire. Boards,
plywood or a ladder should be used to distribute the person's
weight and prevent falling into a burned-out cavity (Figure
2).
Another
firefighter should assist from a safe location nearby. This
person should also wear full turnout gear and should have
a charged hose ready in addition to the hose needed for the
probe.
When
it is believed that the hot spots have been sufficiently cooled,
begin removing the hay from the barn or stack. Keep a charged
hose ready and manned to quickly control any blazing that
may result from missed or insufficiently cooled hot spots.
Hay
which has been damaged by heat, smoke or water should be removed
to a safe location for disposal. Possible uses for damaged
hay include mulch for erosion control on slopes and in gullies.
If uncertain whether heat has damaged hay too much for feeding
have a sample tested.
For
additional information or assistance, contact your county
Extension office.
References
- Bledsoe,
B. L. Systems for Making, Handling, Storing and Feeding
Large Hay Packages, Department of Agricultural Engineering,
University of Tennessee, Knoxville, TN 37901-1071.
- Bruhn,
H. D. and Koegel, R. G. 1985. You Can Avoid Silo and
Haymow Fires. Hoard's Dairyman, June 10, 1985; p 653.
- Murphy,
Dennis and Arble, William. 1986. Extinguishing Silo Fires:
NRAES-18; Northeast Region Extension Agricultural Engineering
Service, Riley Robb Hall, Cornell University, Ithaca, NY
14853.
Smith,
Gary L. 1983. Large Round Bale Fires, Maryland Farm
and Home Safety Newsletter, Sept. 1983, Extension Agricultural
Engineering, University of Maryland, College Park, MD 20742.
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Disclaimer
and Reproduction Information: Information in NASD does not
represent NIOSH policy. Information included in NASD appears
by permission of the author and/or copyright holder. More
NASD Review: 04/2002
This document
is
PB1306
,
a series of the Agricultural Engineering Department, University
of Tennessee Agricultural Extension Service, Knoxville, Tennessee
37901. Publication date: October 1988.
Timothy
G. Prather, Extension Assistant, Agricultural Engineering,
University of Tennessee Agricultural Extension Service, Knoxville,
Tennessee 37901.
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