In 2013, a massive explosion and fire at the West Fertilizer Company near Waco, Texas killed 15 people, including 12 emergency responders. The explosion injured hundreds more. The blast also destroyed hundreds of nearby buildings. The explosion’s force was estimated to equal that of 10 tons of TNT, which would feel like being at the epicenter of a small earthquake.
The fire from the blast spread quickly because the building had no suppression system. Following an extensive investigation, the U.S. Chemical Safety Board concluded that suppression methods would have “helped minimize the severity of the impact of the WFC fire and explosion on the facility and on the surrounding community.”
What is explosion suppression?
Explosion suppression is the automated process of identifying a rapidly accelerating and expanding fire, and then chemically and/or mechanically suppressing it before the situation gets out of control. Ammonium nitrate (a common fertilizer) like that manufactured at the West Fertilizer Company’s plant is a good example of an ignition source material that can provide fuel for an explosion. Any enclosed structure with a lot of dust, grain residue, metals, or other materials can be an explosion risk. That would include facilities such as pharmaceutical plants, chemical factories, refineries, granaries, and wood product manufacturers.
Dust explosions have been a problem since the industrial era. An 1878 dust explosion at a grain mill in Minnesota killed 22, which led to better approaches to ventilation. The introduction of explosion suppression followed. A dust explosion is likely anytime there is:
- A large amount of combustible dust builds up.
- The dust becomes airborne in a confined area.
- There is an ignition source such as a spark.
- An oxidant (usually oxygen in the atmosphere) is present.
Types of explosions
An explosion can be a detonation or a deflagration. Either one can be dangerous because, in each case, pressure waves expand from the center of an explosion and cause rapid burning. With a detonation, there is a shockwave. In the case of a deflagration, there is no shockwave because the occurrence is subsonic, which means it happens slower than the speed of sound. But don’t assume because a deflagration is subsonic that it is slow-moving or less dangerous. Like a detonation, a deflagration grows rapidly and can cause damage in milliseconds.
How does explosion suppression work?
An explosion suppression system immediately mitigates the effects of the event by detecting, controlling, suppressing, and containing. Systems focused on prevention, ventilation, and explosion isolation should also be in place. However, explosion prevention systems include three core elements:
- Specialized sensors for rapid detection.
- Chemical and/or mechanic isolation systems.
- Explosion venting systems.
Just ahead of a fireball is a dramatic increase in pressure. When an explosion occurs within an enclosed space, such as a storage container or duct, sensors immediately detect the pressure change. The sensors signal the control panel, which in turns sends a command to the suppressor containers to dispense the suppressant agent. Chemicals dispersed by the suppression containers act to suck the heat out of the explosion, thereby quickly reducing the dangerously-high temperatures. In less than the time it takes to blink an eye, the fireball has been contained. During this process, mechanical isolation systems may also initiate a high speed knife valve, which forms a protective mechanical barrier within a pipeline.
When explosion suppression systems first became common, halon—a chemical often used in fire extinguishers—was a primary suppression agent. However, halon is now known to have adverse effects on the environment, especially on the ozone. Modern suppression agents have mostly replaced it because they are safer for the environment and people.
The State of Florida follows OSHA guidelines for explosion ventilation, protection, isolation, and suppression. OSHA recommends dust control equipment to include relief ventilation or an explosion suppression system. Other OSHA recommendations focus on ways to prevent explosions from occurring. The design and installation of ducts, dust collectors, and other equipment should be performed with emphasis on preventing leaks so that dust does not escape into the atmosphere. Cleaning work areas of dust buildup should be a part of regular maintenance. A volatile dust buildup of just 1/32 of an inch that covers as little as 5% of a room’s surface can lead to an explosion.
Even with a regular maintenance program, OSHA says buildings with the potential for dust buildup should include an explosion suppression system if maintaining a low-dust, low-oxygen atmosphere is not possible.