Webinar Module - 14 Dec '17.pdf

A Pa s s i o n f o r S a f e t y
UNDERSTANDING
DUST EXPLOSIONS
Consultancy
Training
Testing
Offices in Europe, Asia and the Middle East
COURSE OBJECTIVES
On completion of the course you will learn:
} To understand various conditions of dust explosion
} To understand relevance of various powder properties to dust
explosion
} To understand different available Basis of Safety including
Explosion Prevention, Removal of Ignition Sources and Explosion
Protection.
INTRODUCTION
SIGMA-HSE (INDIA) PVT. LTD.
AREAS OF EXPERTISE
} We bring together our Indian and UK experts to provide our clients
with EHS services and appropriate engineering solutions.
} We undertake Laboratory testing in our UK laboratories to ISO, BSI
ASTM and VDI individual test standards.
Consultancy Testing Training

OUR PRESENCE
} Technical Offices
¾ New Delhi, India
¾ Mumbai, India
¾ Winchester, UK
¾ Abu Dhabi, UAE
} Laboratories
¾ Process Safety Lab, Winchester, UK
¾ The Environmental Laboratory (ELAB), UK
CONSULTANCY SERVICES
Our Consultancy team provides a wide range of specialist technical knowledge
covering the following sectors:
} Process Safety Management (PSM) Implementation
} Industrial Fire & Explosion Hazards
} Electrostatic Hazard Assessment
} Process Hazard Analysis (PHA)
} Functional Safety
} Chemical Reaction Hazards
} Training Workshops
LABORATORY TESTING
} Powder Fire & Explosion Properties
} Gas and Vapor Properties
} Electrostatic Properties
} Chemical Reaction Hazard Testing
SOME INCIDENTS
CTA Acoustics Explosion, Feb 2003
Imperial Sugar Explosion, Feb 2008
Aluminium Dust Explosion, Oct 2003
Do companies really understand the hazards?
It is incidents that reveal the real hazard
But it only happens to other people!! Well… !!

DUST EXPLOSION STATISTICS
CSB presented preliminary data indicating, there have
been 197 Dust Explosion incidents in the United States
since 1980 till 2005, causing 109 fatalities and 592 injuries.
ATEX INTENTION
To provide a coherent focus for controlling risks from
} substances with flammable, explosive and oxidising properties. Today ATEX
also covers Corrosives and compressed gases
} substances which can create potentially explosive atmospheres
} controlling work activities involving other substances that could create a
fire, explosion
No Minimum Amount
CONDITIONS FOR DUST
EXPLOSION

CONDITIONS FOR EXPLOSION
Oxidant
Confinement
Mixing
Fuel Ignition source
CONDITIONS FOR A DUST EXPLOSION
}Dust must be flammable/ combustible and airborne to form a cloud.
}Concentration must be within explosible limits.
}Particle size distribution should be capable of propagating flame.
}The atmosphere need to support combustion.
}Energy related to the ignition source must be sufficient.
IS A DUST FLAMMABLE
} Approximately 70 % of organic powders will
form a flammable atmosphere when dispersed
in air.
¾ Group A powder is FLAMMABLE
¾ Group B powder is NON-FLAMMABLE
} The A/B test only assesses whether a material
is flammable as a dust cloud, it does not
address whether a material is thermally stable
nor whether it can be ignited in a bulk
situation by an external ignition source.
erial
table
Flammable Organic Compounds
70% Flammable 30% Non Flammable
FLAMMABILITY DATA
Powders & Dusts
• Minimum Ignition Energy (MIE)
• Minimum Ignition Temperature (MIT)
• Layer Ignition Temperature (LIT)
• Pmax, Kst, St Class
• Minimum Explosive Concentration (MEC)
• Limiting Oxygen Concentration (LOC)
• Burning Behaviour
• Resistivity
• Charge Relaxation Time
• Thermal Stability

Minimum Ignition Energy (MIE)
} MIE is lowest spark energy spark that can ignite
the optimum mixture of fuel (dust) when
dispersed in air.
} For electrostatic ignition risk analysis, the spark
is generated using a pure capacitive discharge.
} For mechanical ignition risk analysis the spark is
generated using an inductive discharge
(Minimum Ignition Temperature (MIT) value
also required).
} Any ignition source with an energy greater than
the materials MIE, is capable of providing
ignition to the flammable atmosphere.
Minimum Ignition Energy (MIE)
} Starch
} GRP Dust
} Sugar
} Aluminium
} Paracetamol
Blend
100 - 300 mJ
30 - 100 mJ
10 - 30 mJ
3 – 10 mJ
1 – 3 mJ
Minimum Ignition Temperature (MIT)
} MIT is lowest surface temperature
that can ignite the optimum
mixture of fuel (dust), when
dispersed in air.
} MIT is “AIT” for dusts
} MIT is used for both establishing
the maximum permitted surface
temperatures of electrical and non
electrical equipment (with LIT
value) and used with an inductive
MIE value for mechanical spark risk
analysis.
} Ceramic Dust
} GRP Dust
} Starch
} API
} Sulphur
760 °C
560 °C
430 °C
300 °C
200 °C
Minimum Ignition Temperature (MIT)

Layer Ignition Temperature (LIT)
} LIT is lowest surface temperature
that can ignite a 5 mm layer of
material.
} LIT is used for establishing the
maximum permitted surface
temperatures of electrical and
non electrical equipment (with
MIT value).
Layer Ignition Temperature (LIT)
} Pesticide 270°C
} Lycopodium 290 °C
} Wood Fibre 330 °C
} Aluminium > 400 °C
20 Litre Sphere - Explosion Severity
} PmaxMaximum explosion pressure
measured
} Kst Dust Constant (calculated from the
maximum rate of pressure rise (dP/dt)max
} Explosion severity data is required when
an explosion protection system (venting,
suppression or containment) is used or
proposed to be used as a ‘Basis of Safety’.
St Class
DUST TYPE Kst
} Flour 87
} Starch 150
} Aspirin 217
} Pigment 286
} Aluminum 650

Minimum Explosive Concentration (MEC)
} MEC is the minimum quantity of dust,
dispersed in air that is required to form a
flammable atmosphere.
} MEC is measured in the 20L sphere.
} Sometimes the MEC is referred to as the LEL
(Lower Flammable Limit)
} However, as dust clouds are not
homogenous, localised areas within a
dispersed dust cloud (below the materials
MEC) may still give rise to flammable
concentrations.
25
w
< ---- 2 m
---- >
40 g/m3 Coal
Dust
Limiting Oxygen Concentration (LOC)
} LOC is the maximum concentration of oxygen in a mixture of
dispersed combustible dust, air and inert gas, in which an
explosion will not occur
} Generally higher than for gases
} Typically 10 - 15 vol.%
} If unknown, assume 5 vol.%
} (all though this is not cost effective)
} Examples are for N2 as inert gas
MATERIAL LOC(%)
Rye Flour 13.0
Organic Pigment 12.0
Methyl Cellulose 10.0
Beta-naphthol 9.5
Sulphur 7.0
Paraformaldehyde 6.0
Aluminium 5.0
THERMAL STABILITY
Thermal decomposition can lead to:
} Explosion
} Fire
} Fume / smoke emission
} Generation and possible
explosion of flammable gases
} Loss of product quality
SELECTING TESTS FOR SPECIFIC DRYERS
} AIR OVER LAYER – roof of spray dryers and all
dryers where thin deposits occur with air
availability
} AERATED CELL – fluid bed dryers, rotary dryers and
all dryers where air is forced through the material
to be dried
} BULK POWDER (DIFFUSION CELL) – base of large
spray dryers, tray dryers and storage up to 1 tonne.
Areas of bulk powder and low air availability

PARTICLE SIZE
• As the surface area increases so does the explosion violence
• As the surface area increases so the energy for ignition goes down
• Other factors that have an effect are;
• particle shape
• surface structure
The effect of particle size cannot be calculated, testing is the only option!!
10 mm sided square
600 square mm
Divide into 12 x
5 mm squares
Surface area increases
to 1200 square mm
BASIS OF SAFETY
Definition
} The combination of measures relied upon to ensure safety.
} Basis of Safety highlights those aspects of the design and operation
(hardware, protective systems and procedures) that are safety critical.
} It can only be selected once all the significant hazards have been
identified and evaluated.
For Fires & Explosion normally 3 choices;
} Explosion Prevention
} Avoidance of Ignition Sources
} Explosion Protection
WHAT IS A BASIS OF SAFETY
Nestle 2015
WHAT IS A BASIS OF SAFETY
Equipment
Procedures
Deviations
Human Factors
Material Properties
Level of Risk
BASIS
BASIS
of
of
SAFETY

RISK ASSESSMENT
(ATEX Articles 4 & 8)
} Employers should assess and control the risks from dangerous substances.
Employers include contractors, sub-contractors and self-employed people
} Employers must also assess the risks to persons who are not employed by
them but may be at risk from the use of dangerous substances
} With respect to accidents, incidents and emergencies, information,
instruction and training, these duties only apply to non-employees if they
are at the workplace
SPECIAL REQUIREMENTS
Where explosive atmospheres may occur:
} Hazardous area classification is required
} In hazardous areas special equipment must be used
} Hazardous areas must be marked
} The overall explosion safety must be verified
} Appropriate work clothing must be provided
These requirements do not apply where other hazardous conditions
may occur
FAMOUS LAST WORDS
} “We only do it once”
} “We have done it like this for 20 years”
} “It worked perfectly fine at a smaller scale”
01-DUST-26-020318
RECENT FAILURE TO DEVELOP
A BASIS OF SAFETY
IMPERIAL SUGAR

EXPLOSION PREVENTION
• Remove the fuel
- For dusts often not possible
- For gases and vapours, work below LEL
- In some case work above UEL
• Remove the oxidant
- Use inert gas
- Requires LOC data
• Remove all ignition sources
- Not normally achievable in a manufacturing
process
• Use Process Control
- Must be robust
SECONDARY DUST EXPLOSIONS
One of the main hazards associated
with handling dusts is the potential for
devastating secondary dust explosions
1mm Layer of Dust
Bulk Density of
500 kg/m3
100 g/m3
5m
Elimination of Suspensions
} Good housekeeping – If dust is not
lying around it cannot get suspended
which results in an explosive situation.
} Dust on beams is especially a problem
since an explosion in one part of the
facility will cause the dust to be
suspended and exacerbate the hazard.
Stop Releases
Temporary Stop in Duct Open Vessel

Secondary Dust Explosions
} Secondary Explosion Pressure is a Direct Multiplication of Start
Pressure
} Start pressure 1 bar and Pmax is 7 bar then secondary explosion
pressure 14 bar
Secondary Dust Cloud Explosion
ELIMINATE IGNITION SOURCES
} Flames (fire, hot work)
} Hot surfaces
} Electrical installations
} Static electricity
} Lightning
} Mechanical sparks, friction
} Chemical reactions
} Adiabatic compression
} and many others
} Know the ignition sensitivity of
the fuel!
BASIS OF SAFETY
AVOIDANCE OF IGNITION SOURCES - DUSTS
ͻ Minimum Ignition Energy
(MIE – with and without
inductance)
ͻ Minimum Ignition
Temperature (MIT)
ͻ Layer Ignition Temperature
(LIT)
ͻ Further Electrostatic Testing

ELIMINATION OF IGNITION SOURCES
} Can all ignition sources be identified?
}ignition sources that are intrinsic to the process
}ignition sources are not particular to a process
}Is the sensitivity to ignition by these sources known for your
materials?
} Have both normal and abnormal conditions been considered?
EQUIPMENT SELECTION
} Unless, the risk assessment finds otherwise, equipment
and protective systems must be selected as follows:
} Zone 0 and 20
} category 1
} Zone 1 and 21
} category 1 or 2
} Zone 2 or 22
} category 1, 2 or 3
} Equipment must be suitable for gases, vapours or mists
and/or dusts as appropriate
EXPLOSION PROTECTION
Note:
Any of the above require measures to prevent propagation (isolation
measures)
Containment Venting Suppression
EXPLOSION SEVERITY
} Maximum Explosion Pressure
} Explosion Constant, Kst
} St Class

EXPLOSION INDICES
St Class Kst
(bar.m/s)
Description Examples
St 0 0 No explosion Silica
St 1 хϬĂŶĚч
200
Weak explosion Powdered milk, charcoal,
sulphur, sugar and zinc
St 2 хϮϬϬĂŶĚч
300
Strong explosion Cellulose, wood flour, and
poly methyl acrylate
St 3 300 Very strong
explosion
Anthraquinone, aluminium,
and magnesium
EXPLOSION RELIEF VENTING
} Protects plant and personnel from the
effects of an explosion
} Uses weak panels or doors that open
quickly at low pressure
} Panel has to be large enough
} Vent design has many pitfalls for the
inexperienced
(The wrong way)
(The wrong way)

Vented Corn Starch Explosion
CONTAINMENT
} All parts of the plant made strong
} includes pipes, ducts, flanges, covers, etc.
} Must withstand the maximum pressure that is
expected
} Maintain strength over lifetime
} Strong plant is expensive to build and can be
difficult to operate
EXPLOSION SUPPRESSION
EXPLOSION SUPPRESSION
} Injects a suppressing agent into the
vessel as soon as the explosion is
detected
} The explosion is extinguished in the
early stages
} Pressure is still low at that time
} No external effects of explosion

EXPLOSION ISOLATION
} Necessary to prevent pressure piling and
flame jet ignition
} When isolation fails, the explosion in
secondary vessels can be more severe
than the “design” explosion
} explosion protection on secondary vessel
may be insufficient
THANK YOU!
For Queries, contact our Process Safety Expert on +91 9599 024327
or write to him on hchichra@sigma-hse.com
}CONSULTANCY
ƒ Hazardous Area Classification
ƒ Dust Explosion Risk Assessment
ƒ ATEX assessment
ƒ Electrostatic Hazard Assessment
ƒ Process Safety Audit
And OTHERS
PROCESS SAFETY TESTING
ƒ Powder Fire Explosion Properties
ƒ Gas and Vapor Properties
ƒ Electrostatic Properties
ƒ Chemical Reaction Hazard Testing
DETAILED TRAININGS

Webinar Module - 14 Dec '17.pdf

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