Combustible Dust Explosion
Qualitative Risk Assessment:
The conditions determined for a combustible dust to be explosive or not have not been investigated in depth, however it is evident that the explosive or non-explosive condition of a combustible dust, and its explosive characteristics, if it is, are related to the reaction conditions, i.e:
✅The heat power.
✅ The rate of reaction.
✅ The volume of gases generated.
Characteristics of the Explosions.
Dust can occur in bedding and in cloud. Dust in bed is understood as the layers of dust deposited on horizontal surfaces of machines, pipes, windows, floors, etc., of greater or lesser thickness.
layers of dust deposited on horizontal surfaces of machines, pipes, windows, floor, etc., of greater or lesser thickness (0, 1 to several cm.). By
cloud dust means an air-dust mixture, usually affecting large volumes of air and with concentrations that can vary from g/m3 to k/m3.
For the risk of dust explosion to exist, it must be dispersed in the air.
The fundamental characteristics that quantify then the risk of explosion are:
- Minimum explosive concentration.
- Minimum ignition temperature.
- Minimum oxygen concentration.
- Maximum explosion pressure.
- Maximum pressure gradient
Risk Control
The analysis of the phenomena that develop in fires and/or explosions in combustible dusts makes it possible to establish a logical chain applicable to the risk.
Explosion factors:
❌ Conjunction
❌ Conjunction
❌ Factors
❌ Initiation
red_cross: Propagation
❌ Consequences
❌ Prevention
❌ Combating
❌ Evaluation
General Principles of Prevention
Being necessary the coexistence in space and time with sufficient intensity of all the factors already mentioned, the preventive elimination of one or more of them will prevent the onset of any of the two phenomena.
the onset of either of the two phenomena.
**Action on combustible dust.
Action on combustible dust as a preventive measure focuses on two main aspects, which are analyzed below::
A) Limiting the fuel stock.
** This can be achieved by
Scheduling periodic cleaning of workstations, cyclones, pipelines, filters, etc.
Correct design of pipelines (aspirations, transport, etc.).
Maintenance that avoids leaks in ducts.
Localized suction at points where dust is generated.
Avoid free fall when filling tanks.
B) Transforming the dust into non-combustible B) Transforming the dust into non-combustible.
Wet dust handling.
Dust inertization.
The use of an inert powder which, when mixed with the combustible powder, makes the mixture non-flammable is a limited
flammable, is a technique of limited application because it implies contamination of the product.
General Principles of Fighting
It is necessary to adopt as a priority
prevention measures that limit the likelihood of a fire or explosion must be taken as a matter of priority.
explosion.
Unfortunately, the adoption of such measures does not ensure the elimination of the risk of explosion, for the following reasons
risk of explosion, due to the following facts:
⚠ Industrial operations require the movement of dusts.
⚠ Industrial operations require the movement of dusts and it is inevitable that airborne suspensions of dusts will form.
airborne suspensions are inevitable.
⚠ Even if we adopt the most severe preventive measures against the introduction or generation of ignition sources, mechanical or human failures are inevitable.
Fires
Nature of Fire
Fire is the effect produced in a fuel when the necessary heat is applied to it to change from its natural state to another of lower density and in the presence of oxygen. It is a chemical reaction between the vapors given off by a substance (fuel) and the oxygen in the air.
substance (fuel) and the oxygen in the air; or the manifestation of a rapid oxidation with a rise in temperature and emission of light.
Fire, therefore, is caused by the incidence of a heat source that comes into contact with the fuel and initiates the emanation of gases, which ignite when the temperature of their flash points is reached. With this ignition a contribution of calories to the environment is originated, which is added to the already existing heat, coming from the first heat source. This new, higher temperature will affect the fuel
on the fuel, which will cause the release of a greater quantity of gases from the innermost and deepest zones of the fuel.
Fire Chemistry
It is well known that for combustion to take place, three elements must be present: oxygen (comburent), heat and fuel. Hence, it has always been represented graphically by a triangle, in which each of the sides corresponded to each of these elements, giving rise to what is called the triangle of fire.
If any of these elements is not present, combustion does not take place.
All this, has brought as consequence, that modernly it is compared with a tetrahedron when introducing in the combustion process a new element: the chain reaction.
tetrahedron by introducing a new element in the combustion process: the chain reaction, so that each of the faces that make up the tetrahedron are: ✅ Oxygen
: check: Oxygen
✅ Heat
✅ Fuel
:check Chain Reaction.
The explanation of this chain reaction phenomenon is as follows, depending on whether we explain it in chemical terms or in energetic terms.
explained in chemical terms or in energetic terms:
⚠ From the Chemical point of view: **
The initial fuel molecules combine with the oxygen in the air in a series of successive intermediate reactions.
a series of successive intermediate reactions (chain reaction), until they reach the final products of combustion.
⚠ From the energetic point of view.
All reactions occurring in this field are exothermic (they give off heat).
(they give off heat), hence the energy given off is sufficient to release other electrons from the fuel atoms and, therefore, the development of the chain reactions.
of the chain reactions.
Fire Rating
For extinguishing purposes, not all fires are the same; they will depend on the type of fuel that burns, so that they behave in one way or another.
According to the fuel that burns: Class A: Includes fires of solid materials, generally of the organic type.
Class B: Includes fires involving liquids or solids which, by the action of heat, turn into liquids and greasy solids: gasoline, oils, paints, greases, etc.
Class C: Includes fuel gas fires: propane, butane, city gas;
etc.
Basic Extinction Principles
As previously mentioned, fire would be extinguished if by any procedure any of the elements that produce it were eliminated, namely: Oxygen, Heat, Fuel and Chain Reaction.
Dilution.
From a theoretical point of view, it is the most effective and direct method: however, the enormous practical difficulties involved in its application (imagine a fire in a large warehouse full of merchandise that would have to be evacuated to avoid
However, the enormous practical difficulties involved in its application (imagine a fire in a large warehouse full of merchandise that would have to be evacuated to prevent it from spreading) make it practically unfeasible and little used.
Cooling.
It consists of removing heat to reduce the temperature of the fuel. The fire will be extinguished when the surface of the burning material cools down to a point where it does not emit enough vapors to maintain a mixture that initiates or maintains combustion (ignition temperature).
Smothering *
Prevents combustible vapors that are released at a given temperature for each material from coming into contact with oxygen in the air.
temperature for each material, from coming into contact with the oxygen in the air.
It can be achieved by displacing the oxygen by means of a certain concentration of inert gas, or by covering the fuel with some substance.
Breakage of the chain reaction.
It prevents the transmission of heat from one fuel particle to another,
interposing catalytic elements between them.
These are chemical compounds, which react with the free radicals, neutralizing them.
neutralizing them.
Workplaces and Work Spaces - Confined Space Work.
Workplaces and Spaces
Constructive Conditions Constructive Conditions.
The design and constructive characteristics of workplaces shall be such as to offer adequate safety against the risks of: Fall of persons to the same and different levels, collisions against immobile objects, stepping on objects, run over or
collisions with vehicles, collisions with moving objects and falling objects due to collapse or collapse.
Structural Safety
Workplace buildings and premises must be of adequate structure and strength for their type of use.
adequate for their intended use. Thus for their intended use, all structural or service elements, including working platforms, stairways and ladders,
shall:
Have the necessary solidity and strength to withstand the loads or stresses to which they will be subjected.
to which they are subjected.
Have a reinforcement, fastening or support system that ensures their stability.
stability.
Working Spaces and Hazardous Areas
The dimensions of workplaces must allow workers to perform their work without risk to their safety and health, and in acceptable ergonomic conditions.
acceptable ergonomic conditions. The minimum dimensions shall be:
- The height from the floor to the ceiling shall be 3.00 meters, with 2.50 meters allowed in commercial, service, service, and industrial premises.
2.50 meters in commercial premises, services, offices and offices.
Floors and Openings
One of the main causes of accidents due to floors is slipping,
It is therefore very necessary to assess the danger of slipping on the surface of the different types of floors.
Order and cleanliness*
Order is necessary to achieve a more efficient use of the available space, and it is always an important complement to the means of protection.
First aid materials and premises.
Workplaces shall have materials for first aid in case of accident, which shall be adequate, in terms of quantity and characteristics, to the number of workers, to the risks to which they are exposed and to the facilities of access to the nearest medical assistance center.
access to the nearest medical assistance center. The first aid material must be adapted to the professional attributions of the personnel authorized to provide it.
to provide it.
Confined Spaces
These have been defined as those spaces sufficiently enclosed so that any hazardous air contamination present therein cannot be avoided or eliminated by natural ventilation through existing openings.
by natural ventilation through existing openings.
Thus, in addition to the absence of means of natural ventilation, a space may be considered confined when:
(a) The volume is so small that even the uniform diffusion of gases or vapors throughout the space would not prevent the formation of a toxic concentration in the breathing zone of the operator.
a) The volume is so small that even the uniform diffusion of gases or vapors throughout the space would not prevent the formation of a toxic concentration in the breathing zone of the operator; or lack of oxygen; or flammable/explosive environment.
b) There are no other workers in the vicinity to watch and assist the
operator in case of emergency.
c) The openings are so small or so far away that it is difficult to penetrate or exit to remove an
penetrate or exit to remove an
Risks in Confined Spaces
Given the particular characteristics of these premises, this section will identify the risks inherent to confined spaces and their description, on the understanding that there are also risks of a general nature that any activity can generate when carried out in any place, regardless of the type of place.
When working in a confined space, a distinction can be made
distinguish between three groups of risks differentiated according to the work environment
work environment:
General risks, which will be generated regardless of the existing atmosphere.
the existing atmosphere.
Atmospheric risks, which are directly related to the atmosphere in the work area.
Atmospheric risks, which are directly related to the existing atmosphere in the work area.
Risks "of people", specific to the workers involved.
CONFINED SPACE ENTRY PROCEDURE.
1º.- Isolation of the confined space against various risks.
2º.- Examine the equipment
3º.- Delimitation of the work area.
4º.- Checking of the interior atmosphere.
5.- Recording of the results
6 .- Opening of the confined space, if any
7.- Evacuation of gases or vapors. Ventilation
8.-Test the confined space atmosphere again.
9.- Record
10.- Establish a means of escape/rescue.
11.- Enter the confined space and do continuous sampling to ensure that there is not an insufficient or
that there is not an insufficient or excessive concentration of oxygen or the presence of toxic substances.
12.- Start work
Construction Safety
Work Teams
Within the term work teams, some groups have been identified which, either because of the singularity of their members, or because of the generality they represent,
constitute elements worthy of particularized study.
Hanging Scaffolding
Earth Moving Machinery
Work in proximity to power lines
The minimum safety distance for work in the vicinity of high-voltage, medium-voltage installations (measured between the nearest live point and any extreme part of the operator or the tools and materials used by the operator).
extreme part of the operator or of the tools and materials he uses).
Preventive measures
If the safety distances cannot be maintained, other preventive measures should be taken.
other preventive measures should be taken
Line Discharge
Withdrawal of the line or conversion to subway
Insulation of line conductors
Installation of safety devices
Interposition of obstacles in the work area
Medidas de Información
La señalización se efectuará mediante:
• Cintas o banderas de color rojo.
• Señales de peligro o indicadores de altura máxima.
• Alumbrado de señalización para trabajos nocturnos.
Excavations
In excavations and in the work carried out in them, the main danger arises from
the main danger arises from accidental movements of the ground that cause the ground that cause landslides, landslides, subsidence
causing landslides, landslides, collapses and subsidence of the works,with the consequent burial of people.
Before starting work, it is necessary to be aware of a series of circumstances that may affect the safety of the work.
Before starting the work, it is necessary to be aware of a series of circumstances that may affect the safety of the work:
a) Characteristics of the ground in relation to the works to be carried out, such as: natural slope, bearing capacity, water table, moisture content, possibility of filtrations, stratifications, previous alterations of the ground, etc.
b) Proximity of buildings and characteristics of their foundations, as well as possible overloading in the vicinity.
as well as possible overloading in the vicinity of the excavation walls.
c) Existence of vibration sources (roads, factories, etc.).
d) Existence or proximity to water, gas, electricity and sewage installations.
sewerage.
Personal and Collective Protection Equipment
Types of PPE.
The great variety of the parts of the body of the person to be protected means that there are many types of equipment to be used, and many characteristics to be taken into account.
characteristics to be taken
Due to the limitations of a manual, it would be impossible to point out each and every one of them, so the most important aspects that should be taken into account will be presented, referring to the technical standards in force in case there is a need to go deeper into a particular piece of equipment.
Protective Helmets
Foot and Leg Protection
Eye Protection
Hand Protection
Protective Clothing