The food industry experiences more combustible dust explosions than any other industry due to commonly held perceptions that food is safe. However, many food products can combust if particulate levels exceed minimum explosive concentrations. While OSHA has no dust explosion standard, NFPA provides guidelines. Key factors that enable dust explosions include an ignitable concentration of dust dispersed in air. Common protective measures include venting, suppression, containment and isolation of dust. Poor housekeeping allowing fugitive dust accumulation presents significant risks for secondary explosions. Recent major food industry dust explosions demonstrate the devastating costs of unaddressed hazards. Effective protection requires balancing food safety and explosion prevention requirements.

1. Explosion Protection in
the Food Industry
Teresa Long
November 2012

2. OSHA Standards
According to OSHA statistics, the food
industry has twice as many combustible
dust related fires and explosions than any
other industry
 74 incidents between 1980 and 2008
 There is no OSHA Combustible Dust
Standard

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3. NFPA Standards
NFPA 61 “Standard for the Prevention of Fires
and Dust Explosions in Agricultural and Food
Production Facilities”
 NFPA 68 “Guide for Venting of Deflagrations”
 NFPA 69 “Standard on Explosion Prevention
Systems”
 NFPA 654 “Standard for the Prevention of Fire
and Dust Explosions from the Manufacturing,
Processing, and Handling of Combustible
Particulate Solids”

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4. You Can Eat It, So It’s Safe

Often, the hazard isn’t recognized

Food is perceived to be safe
Minimum Explosible Concentration (MEC)
of many food products is <100mg / m3

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5. Combustible Products
Egg white
Milk, powdered
Milk, nonfat, dry
Soy flour
Starch, corn
Starch, rice
Starch, wheat
Sugar
Sugar, milk
Parsley(dehydra
ted)
Green coffee
Hops (malted)
Lemon peel dust
Lemon pulp
Locust bean gum
Xanthan gum
Wheat grain dust
Peanut meal and
skins
Raw yucca seed
dust
Sunflower seed
dust
Oat flour
Oat grain
dust
Olive pellets
Onion
powder
Peach
Potato
Potato flour
Sugar (10x)
Potato starch
Rice dust
Rice flour
Rice starch
Rye flour
Semolina
Soybean dust
Spice dust
Spice powder
Tapioca
Sunflower
Walnut dust
Wheat flour
Wheat
starch
Malt
Whey
Sugar, beet
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6. Recipe for a Dust Explosion
Five elements, which
form the explosion
pentagon, must occur
simultaneously for a
dust explosion to occur.
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7. Simultaneous Conditions Required for Dust Explosions
The dust must be combustible
 The dust must be dispersed
 The dust concentration must be within the explosible
range (above the Minimum Explosive Concentration,
MEC)
 The dust must have a particle size distribution capable of
propagating flame
 The atmosphere in which the dust cloud is present must
be capable of supporting combustion (oxygen)
 Ignition source must have sufficient energy to initiate
combustion (Minimum Ignition Energy, MIE)

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8. Dust Explosion Protection Principles
(Ebadat, 2012)
Risk of an explosion is minimized when one of the following
measures is ensured:





An explosible dust cloud is never allowed to form
The atmosphere is sufficiently depleted of oxidant (normally the
oxygen in air) that it cannot support combustion
All ignition sources capable of igniting the dust cloud are removed
People and facilities are protected against the consequences of an
explosion by “protection measures” such as explosion containment,
explosion suppression or explosion relief venting
Housekeeping activities must ensure that secondary fuel sources are
not available. Of key importance is the evaluation of dust release
points and exhaust ventilation needs
–
It is much easier to replace a gasket, install local dust aspiration systems, etc.,
than to spend the time cleaning up the dust that has escaped
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9. Explosion Protection Measures
Explosion relief venting
 Explosion suppression
 Explosion containment
 Explosion isolation
 Inert gas purging, if needed

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10. Housekeeping and Ventilation
System Design







Most serious dust explosions are not caused by a primary explosion inside
the plant, they are caused by a secondary explosion within the building
An initial event causes pressure and shock waves to propagate into the
workplace, and dust deposits form a cloud, which ignites.
If this happens in a series of connected rooms, a chain reaction occurs and
the result can be devastating
Secondary dust explosions are common in industries such as the food
industry where the material are perceived to be safe. Dust is often present
outside the process equipment due to the perception the material is toxic
and cheap
Fugitive dust outside equipment must be minimized. Evaluation of dust
release points and exhaust ventilation needs is critical
Preventing dust is much easier than cleaning up after it has escaped.
Venting inside a building can cause harm to people, damage the facility,
and poses an increased risk of a secondary explosion
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11. Process Equipment Design
Source: New Zealand Department of Labor
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12. Ventilation Ducting






Ducting carrying product + air is vulnerable to primary explosions
Four elements of the explosion pentagon are present: fuel, oxygen,
confinement, and suspension
All that is needed is an ignition source
Ducts to transport dust are designed to operate at ~4,000 ft/min
(~45 mph or ~20 m/s ) in order to keep the dust entrained
In a closed vessel, such as a duct, expansion cannot occur and
pressure rises
In a long duct, an explosion can propagate. Expansion of the dust
increases turbulence, which increases combustion rates, and the
explosion accelerates (2km per second) until a detonation is
reached
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13. Safety Measures




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Do not locate dust collectors inside buildings
Rooms, buildings, and dust collectors should have explosion relief
venting distributed over the exterior wall of buildings and enclosures
Explosion venting is directed to a safe location away from
employees
The facility should have isolation devices to prevent deflagration
propagation between pieces of equipment connected by ductwork
Dust-containing systems (ducts and dust collectors) should be
designed in a manner that fugitive dusts are not allowed to
accumulate in the work area
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14. The Dilemma
“The food industry has potentially conflicting requirements
for food safety (hygiene, cleanability and prevention of
foreign matter contamination) and explosion safety
(venting, suppression, isolation). Finding a safe path through
these requirements is not easy, and the blanket application
of non-food industry solutions to food processing is often not
practical”
Dr. Christopher Bloore, Dairy Industry Systems Consultant to
the New Zealand and Australian Dairy Industries
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15. The Dilemma
Explosions are costly and can be just as
devastating to a company’s image as
contaminated food in the supply chain
"Relying on housekeeping as a first line of defense against
explosion and fire is a false economy - not only is there a
greater risk to the workers, but the maintenance costs for
machinery are higher, due to increased abrasion from dust
getting into the moving parts of machinery"--Eric
Anderson, P.E, Ventilation Engineering
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16. Imperial Sugar
(February 7,2008)



14 killed, 36 injured, extensive
damage to the plant
Resulted from ongoing
releases of sugar from
inadequately designed and
maintained dust collection
equipment, conveyors, and
sugar handling equipment
Minimum explosible
concentration in air: 0.045 g/l
Source: CSB
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17. DeBruce Grain Elevator
Explosion June 8,1998
7 killed, 10 injuries
Grain dust accumulation in pneumatic dust collecting duct
North silo complex as seen from the headhouse
South end of north silo complex viewed from the west
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18. DeBruce Grain Elevator
Explosion June 8,1998
Wall damage on East side of headhouse
Headhouse with truck dump, lean-to, and dust collection system
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19. DeBruce Grain Elevator Explosion
Possible transition from deflagration (subsonic burning) to
detonation (supersonic burning) in the combustion process
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20. LiHua Starch Co. Qinghuangdao, China
21 killed, 47 Injured
February 24, 2010
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21. LiHua Starch Co. Qinghuangdao, China
21 killed, 47 Injured
February 24, 2010
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22. Lucky Day
Tapioca Explosion Thailand
July 7, 2011
9 injured
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23. References
Anderson, E. (10, 28 2012). [Personal Interview].
Bloore, C. (10/15/2012). [Personal Interview].
Zeeuwen, P. "Explosion Risks in Silo Filling and Discharge." Chilworth Technology. N.p.. Web. 27 Oct
2012.
Ebadat, V. "Dust Explosions In The Food Industry." Food Manufacturing. 2012: n. page. Web. 27 Nov.
2012. <http://www.manufacturing.net/articles/2012/03/dust-explosions-in-the-food-industry>.
New Zealand. Department of Labor. APPROVED CODE OF PRACTICE FOR THE PREVENTION,
DETECTION AND CONTROL OF FIRE AND EXPLOSION IN NEW ZEALAND DAIRY INDUSTRY SPRAY
DRYING PLANT ISSUED. 1993. Print.
Haywood, B. "Dust Explosions In The Food Industry." SAFTENG.net. N.p., n. d. Web. Web. 03 Nov.
2012. <http://www.safteng.net/index.php?option=com_content&view=article&id=2000&Itemid=4>.
Grain Elevator Explosion Investigation Team, . United States. OSHA. DeBruce Grain Elevator Explosion
- Report. 2003. Web. <http://www.osha.gov/SLTC/grainhandling/geeit/index.html>.
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