combustible dust awareness - airah

Combustible Dust AwarenessDavid McEwanSolutions Sales Manager – Extraction & Filtration Technologies – Aust/NZCombustible Dust applications Manager – APAC / Australia

IntroductionAustralia and New Zealand are lucky to have had very few dust explosions and only a handful of reported deaths as a direct result of combustible dust incidents.

There IS an Australia / New Zealand code for handling of combustible dusts.AS / NZS 4745:2012 Code of practice for handling combustible dusts.AS / NZS 4745:2012 refers directly to VDI3673 – German (precursor to EN14491 – European) and NFPA68, NFPA69 (USA)

Combustible dust awareness is as much about risk assessment as it is the practical side to supply and installing safe equipment.

In risk assessment, anecdotal evidence does not constitute fact. If you complete a risk assessment, and a dust explosion occurs and you lose control – you were wrong!

Dust explosions don’t come with a warning they’re about to happen.But with appropriate understanding of risks and management of the potential, a safe installation can be achieved.

Combustible Dust Awareness

Its only a ‘little bit of dust’

• Some dust generating processes produce a very small amount of dust.

• Example:

• Bulk bag filling decanting into 20 kg bags, dust extraction collects around 3 g of dust per fill operation

• Slowest operator runs at 2 bags per minute -> 120 bags per hour

• 8 hour shift 960 bags per day at 3 gram of dust per bag = 2.88 kg per shift.

• Dust collector has 100 ltr bin, using a bulk density of 600 kg/m3 bin holds 60 kg

• So the operator empties the bin every second Friday when it appears half full.The bin will contain approx. 28 kg of powder

• The air movement inside the dust collector keeps some of the dust in a cloud so there is always a combustible dust cloud inside the collector.


Its only a little bit of dustCombustible Dust Awareness

Fire TriangleTo cause fire, you need fuel, oxidiser, sufficient ignition source.

Which can you control?


IntroductionAdd constant dust cloud from air movement causing dispersion cloud within the collector, and containment from the dust collector enclosure and now we are trying to contain the overpressure which may result from a dust cloud ignition.


Dust extraction1. Dust collection system has one purpose – extract the airborne ‘nuisance dust’ from workspace.

This purpose serves several system goalsa. improve the provide a safe workplace for operators to breath clean air.b. hazardous area reduction.c. improved hygiene and reduce cross contamination.

2. The dust collector conveniently extracts the nuisance dust from process, potentially many different sources.a. will these dusts react with each other?b. will one dust react with another to be the ignition source?c. what is the worst case of these powders mixing

could the small concentration of a combustible dust amongst inert powders actually reduce any dust cloud risk? **

3. Once we have collected the dust(s) into one location, what housekeeping / engineering risks does this present?a. handling combined dustsb. reactions between dusts and by-products

** it is important to establish that there is no chance of the combustible dust only being extracted and that the blend is constant.From a risk assessment view, this action is very dangerous as the blend of powders cannot be guaranteed.


Dust extraction – reduce the risks1. Engineering Controls

Can we remove the fine dust from the process? Reduce the available fuelCan the fuel load be reduced by feeding out the powder or regular housekeeping?Can we use physics to change air speeds and reduce chance of dust cloud forming?Can the ‘risk powder’ be mixed with other inert powders? Can we separate the process which may supply ignition source to the system?Is one extraction system the answer?

2. Can we admin the risk awayChange operator process to remove ignition source or fuel from extraction.Operator training / single point lesson.

3. Can we relocate the dust extractor to a safer location with exclusion zone to safe area?


Duct Velocity – system design - housekeeping

Internal duct velocities should be such that dust cannot settle in the duct.

Correct duct velocities means the internals of the duct stay clear and design duct areas remain, maintaining speeds and design pressure losses.

Using VSD to reduce flow in dust extraction systems must maintain minimum velocities.

If dust settles it can take 3 times the carrying velocity to re-entrain dust into the airstream.


Don’t poke the bear….

Some TerminologyKst – maximum rate of pressure rise in a closed system.Kst is determined by (dp/dt)max.V1/3 (explosion behavior of a combustible dust in a closed system).

Pmax – maximum pressure reached in the combustible dust test, if Pmax exceeds 0.4 bar, it is said an explosion has occurred.

St rating – categories for Kst valuesSt ratingSt1 – a dust with a tested Kst within the range Kst1 to Kst199Example, wood dust 95, soap 111, sugar 132, polyethylene 134, printer toner 196.

St2 – a dust with a tested Kst within the range Kst200 to Kst 299Example, polyester 237, wood flour 224, paint powder epoxy 202, corn flour 200

St3 – a dust with a tested Kst of 300 or aboveExample, magnesium 508, aluminium powder 300, ’hybrids’


Is my dust combustible?• Explosibility Parameters

• Dust Cloud reactivity (Kst, how fast, and Pmax, how big)

• Minimum Dust Concentration / Low Explosion Limit (how much)

• Ignition Characteristics

• Dust cloud minimum ignition energy (MIE – energy level needed)

• Dust cloud minimum ignition temperature

• Dust layer minimum ignition temperature

• Over 70% of dusts are generally considered combustible in the right conditions.


What dusts are combustible?Combustible Dust Awareness

StandardsUnder AS NZS 4745:2012 a risk assessment of the application is to be completed in line with AS/NZS31000 and AS/NZS 3931.If a risk is identified, either a preventative or protective system will be designed and installed.

• Test the Dust or Research the application

• Simtars (Brisbane) can test dust properties

• http://staubex.ifa.dguv.de/?lang=eInstitute for Occupational Safety and Health of the German Social Accident Insurance

• Evaluate the Worst Case

• When mixing powders, use the highest risk as dimensioning data.

• Understand the Regulatory Requirements.

• Ensure installations meet standards as well as equipment.

• Engage a Combustible Atmospheres expert.


http://staubex.ifa.dguv.de/?lang=e

Dust PropertiesEach dust has its own properties, note the different Kst values for same particle size dust


Industry AwarenessFirst combustible dust incident recorded 1785, Turin, Italy.

In 2003, 3 major events in USA prompted the chemical safety board to investigate.

West Pharmaceuticals 6 fatalitiesDozens injuredHundreds of jobs lost

CTA Acoustics 7 fatalities44 InjuredExtensive facility damage

Hayes Lemmerz International 1 fatalities3 InjuriesExtensive facility damage


Industry AwarenessDec 26, 2018 Beijing China

http://global.chinadaily.com.cn/a/201902/14/WS5c64c3c4a3106c65c34e93fa.html

On December 26, 2018, students from the urban planning and environmental engineering department were carrying out sewage treatment experiments when an explosion occurred, killing three of the students.

Multiple government departments carried out a joint investigation of the incident and found that university students had acquired dangerous chemicals and carried out high-risk experiments that violated school regulations. The investigators said that university personnel failed to properly oversee the safety of laboratories and scientific research projects.

They found that while the students were stirring phosphoric acid and magnesium powder in a mixer, a spark caused by metal friction ignited the hydrogen generated in the hopper, causing an explosion. This led to a magnesium dust explosion.

Public security authorities confirmed that the director of the research project and the manager of the laboratory will be investigated for criminal negligence. The Ministry of Education and Beijing JiaotongUniversity punished 12 officials from the university and authorities have ordered comprehensive safety inspections at every stage of the production, sale, transportation, and storage of dangerous chemicals.

All Beijing universities must now carry out safety inspections and take other corrective measures, such as improve laboratory safety management systems and improve personnel training.


http://global.chinadaily.com.cn/a/201902/14/WS5c64c3c4a3106c65c34e93fa.html

Industry AwarenessIn 2008, single major event in USA prompted landmark investigation

Imperial Sugar event 14 fatalities38 Critical injuriesExtensive facility damageUS$8.8M fine from OSHA

Between 2008 and 2012, CSB documented 50 examples of combustible dust accidents.

Each event occurred in a manufacturing or processing facility where the site owners had ignored obvious risks.

Ignoring the risks resulted in 29 fatalities and over 150 injuries.


Industry AwarenessOther documented events

Halifax Grain Elevator explosion Aug 2003

Westwego Grain Elevator explosion Dec 197736 fatalities

OSHA investigated 25 years of cases between 1976 and 2012503 explosions677 injuries184 deaths


Industry Awareness2003, Gunnedah NSW. Saturday evening, 7:50 pm, pet food factory boiler fails, which exploded gas bottles, which exploded wheat dust.

Cost $10 Million

35 Jobs lost.

30 homes damaged, some shifted from their foundations.

Damage radius 1.5km


Industry AwarenessAugust 2, 2014, 7:37 amKunshan, Jiangsu province.Zhongrong Metal Production CompanyPolishing metal (aluminium) wheels for GMH

265 employees present at time of event44 fatalities at scene, another 31 in local hospital that day71 further fatalities between August and Dec 2014.

114 registered as injured.

19 months later, more than 70 victims still being treated in local hospitals.

Final toll over 200

Client had been warned the dangers but ignored risks.

3 executives were charged along with 11 government officials.Sentences from 3 years to 7 ½ years.


Incidents locationCSB investigated 281 further incidents between 1980 and 2005.

44 different states, various applications, various dusts.


Global loss by IndustryWood, food and Metal are responsible for 65% of global reported events.


Explosion relief ventingCalculate the area of explosion relief panel required.

Allow for the explosion panel to discharge into a safe area

European Standards (EN)

Horizontal exclusion zone, fireball length is 10V1/3

For a 1m3 vessel, fireball length is 10 mtr

For a 4m3 vessel, fireball length is 15.9 mtr

Vertical exclusion zone, fireball length is 8V1/3

For a 1m3 vessel, fireball length is 8 mtr

For a 4m3 vessel, fireball length is 12.7 mtr

NFPA (USA) standards 10 x V1/3 for metal dust, 8 x V1/3

for organic dust, divided by the number of equally spaced explosion vents


12 m3 vessel, starch (organic) powder, controlled event.Flame length 23 mtr.

Controlling a dust explosion1. Build a vessel that can contain the increase in pressure.

2. Let the pressure out, create a weak point – explosion relief vent.Creates a control point by being able to predict the exit path.

3. Remove the oxygen from the vessel.


Controlling a dust explosion1. Ensure the design is able to handle the dust


1. Explosion Vent Ductingless than ½ Hyd diam in length has no effect on explosion vent area calculations.

Explosion Vent Ducting

Explosion Ducting

Combustible Dust Awareness – Flameless Venting RSBP Flex for reduced safety zones and indoor applications

Protecting workspaceEven if a dust collector is fitted with correctly sized explosion relief venting, a flame front can be forced back up the inlet duct and travel back down the duct to the workspace.


Compliant System (relief venting)


Passive isolation valve

Explosion relief vent Active isolation valveRapid abort gate

Sensor to activate Rapid abort gate

Ex rated rotary valve

Duct strong enough to contain pressure increase

Explosion relief venting

Locate explosion panels safely


Upward Venting Auto MZ

Evaluate • Know the dangers:

• Does process or components increase risk?

• Can improvements / changes reduce the risks?

• Test or Research the dust properties

• Complete Dust Hazard Analysis or Combustible Dust Document.

• Evaluate the Worst Case:

• ‘If you complete a risk assessment, and someone gets hurt, your risk assessment was wrong’.

• Understand the Regulatory Requirements

• Use certified equipment and safety devices.

Extract the combustible dust from the workspace.Control the potential fireball by discharging vent to a safe area.

Isolate the potential risk by keeping any event away from workspace.Monitor the activation of safety devices – stop process.


Should it take a disaster to make a change?


StandardsAS NZS 4745 Code of practice for handling combustible dusts

AS NZS 3931 Risk analysis of technological systems – Application guide

AS NZS 31000 Risk Management Standard

NFPA 68 Standard on Explosion Protection by De-flagration Venting – review due early 2018

NFPA 69 Standard on Explosion Prevention Systems

NFPA 484 Standard for Combustible Metals

NFPA 652 Standard on the Fundamentals of Combustible Dust

NFPA 654 Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Parti culate Solids

NFPA 664 Standard for the Prevention of Fire and Dust Explosions in Wood Processing and Woodworking Facilities

EN 14491 Dust Explosion Venting Protective Systems

EN 16447 Explosion Isolation Flap Valves

EN 15089 Explosion Isolation Systems

EN 14373 Explosion Suppression Systems

EN 14034 Explosion characteristics of dust clouds

VDI 3673 Pressure release of dust explosions

AS/NZS 60079 Australian Hazard Area Standards

AS/NZS 80079 Explosive atmospheres (sect 36, non electrical components)


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combustible dust awareness - airah

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