Teresa LongNovember 2012

Explosion Protection in the Food Industry

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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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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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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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Combustible Products

Egg whiteMilk, powderedMilk, nonfat, drySoy flourStarch, cornStarch, riceStarch, wheatSugarSugar, milkParsley(dehydrated)

Green coffeeHops (malted)Lemon peel dustLemon pulpLocust bean gumXanthan gum Wheat grain dustPeanut meal and skinsRaw yucca seed dustSunflower seed dust

Oat flourOat grain dustOlive pelletsOnion powderPeachPotatoPotato flourSugar (10x)

Potato starchRice dustRice flourRice starchRye flourSemolinaSoybean dustSpice dustSpice powderTapioca

SunflowerWalnut dustWheat flourWheat starchMaltWheySugar, beet

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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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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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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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Explosion Protection Measures

Explosion relief venting Explosion suppression Explosion containment Explosion isolation Inert gas purging, if needed

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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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Process Equipment Design

Source: New Zealand Department of Labor

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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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Safety Measures 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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“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

The Dilemma

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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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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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DeBruce Grain ElevatorExplosion June 8,19987 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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DeBruce Grain ElevatorExplosion June 8,1998

Headhouse with truck dump, lean-to, and dust collection system

Wall damage on East side of headhouse

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DeBruce Grain Elevator Explosion Possible transition from deflagration (subsonic

burning) to detonation (supersonic burning) in the combustion process

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LiHua Starch Co. Qinghuangdao, China21 killed, 47 Injured February 24, 2010

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LiHua Starch Co. Qinghuangdao, China21 killed, 47 Injured February 24, 2010

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Lucky DayTapioca Explosion Thailand

July 7, 2011 9 injured

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ReferencesAnderson, 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>.