Before talking about the protections that industrial equipment must have when we work with dangerous substances, we must consider some key definitions that will help us better understand the topic.
What is an explosion?
The EN-1127-1 standard defines an explosion as a sudden oxidation or decomposition reaction with an increase in temperature, pressure or both, in other words, is a combustion that will be faster or slower in a gas or dust.
Some of the effects of an explosion are:
- Loud noises and pressure impacts that can cause walls to collapse and windows to break.
- Heat radiation and smoke gases.
- Flame fronts.
How does an explosion occur?
For there to be an explosion there must be:
- A flammable substance (flour, steam, or gases).
- Oxygen.
- Ignition source (spark).
- Confinement (in the handling of combustible dusts).
- Suspension (in the handling of combustible dusts in the form of flakes, filaments, fibers, scales).
What is a deflagration?
It is when combustion occurs at a speed of (0.5 to 1) m/sec, releasing large amounts of heat, flames and a wave of pressure.
What is a detonation?
It is when the deflagration travels through pipes reaching supersonic speeds, not generating flames but a very strong shock wave (audible) that is difficult to control anymore that the pressures and speeds are very high, generating great damage, both civilian and human (secondary explosions).
What is a combustible dust?
NFPA 654 defines combustible dust as a solid particulate that presents an independent risk of fire, deflagration, and detonation of size and shape, when suspended in air (or other oxidizing medium) at various concentrations.
As technology and the industry in general advance, the protection systems that must be in place also advance as we know the risks when working with powders industrial.
To the question, why is it essential to have an explosion protection system? The answer is simple, due to the nature of the dust with which we work, except that its destructive capacity is often unknown. Coffee dust, sugar, wood, metal, etc. They can be classified as explosive or non-explosive (Go or No Go). When the dust we work with is explosive, we must ask ourselves, How explosive is the dust we work with? The answer to this question to the following variables mentioned.
KST and Pmax, the variables that can be deadly
NFPA standard 652 (2019) talks about a cataloging or explosiveness indices depending on a quantitative value of KST. But first, what is KST and Pmax?
The KST is defined as the explosiveness index and is characterized by how quickly a limit pressure (Pmax.) is reached after a ignition in uncontrolled combustion. If the Pmax is reached in the container in which combustion takes place. The destruction of the container that houses it is imminent since it is not, in many cases, designed for these pressure limits. The KST can be defined by the following formula:
KST = (DP/DT)max * ∛(V)
In other words it can be deduced from the following image:
The units of KST are related to (bar*(m/s)), once again showing the speed (slope on the graph) to reach its maximum limit of pressure (Pmax.) So the NFPA 652 (2019) standard can help deduce with the following image how explosive a powder is or not.
Let’s look at a simple example of the difference that can occur between two products:
The units of KST are related to (bar*(m/s)), once again showing the speed (slope on the graph) to reach its maximum limit of pressure (Pmax.) So the NFPA 652 (2019) standard can help deduce with the following image how explosive a powder is or not.
Let’s look at a simple example of the difference that can occur between two products:
In our example, if we compare the KST levels of soybeans and aluminum, we could conclude that aluminum is more explosive than soybeans if we subject it to the same container. Therefore, different protection should be considered for each equipment in the presence of different dusts; In our case, greater protection for the equipment in the presence of aluminum. The containers they house are not designed to reach the pressures generated by the dusts in the combustion process, therefore when they break, particulate matter can travel, causing great civil damage and even the death of people. The real problem lies in the fact that there is still not enough awareness of the imminent danger that exists and it is unknown that, for example, in the year 2023, 53 explosions were recorded around the world.
Explosion protection
NFPA 654 establishes methods for hazard identification and appropriate measures for work areas based on three basic premises:
- Preventing the formation of a hazardous atmosphere: Cleaning
- Prevent ignition: With the use of temperature sensors to avoid overheating of moving parts such as bearings, reduction of oxygen using nitrogen, dilution of combustible dust with other non-combustible dust, using local regulations for proper landing of equipment.
- Control: Limiting the consequences of the deflagration with mitigation (vent panels), with active protection (suppressor equipment based on sodium bicarbonate) and/or chemical isolation (suppressors) or short valves fire.
FIKE: Life Safety and Protection of Critical Assets
Fike, a company with more than 75 years in the market, offers insulation solutions, suppression and venting of explosions, according to the needs and budget of the clients.
A dust explosion can cause significant downtime, increased insurance premiums, fines, damage to equipment and buildings, and what’s more worse, damage to employees. Fike’s ability to identify your risks and provide the necessary solutions protects both businesses and workers from the dangers of combustible dust.