Whether you’re a manufacturing veteran or just getting started with a new facility, the National Fire Protection Association’s (NFPA) complex web of regulations can be difficult to navigate on your own. To help you get acquainted with the rules as they apply to rotary valves and processing, we put together a handy glossary of NFPA and fire safety terms.
And no, we didn’t use all 26 letters of the alphabet — we only included what we think you need to know. (Besides, we challenge anyone to come up with an NFPA term that starts with “X.”)
A is for Airflow
Rotary airlocks seal the airflow between the inlet and outlet of your valves, allowing material to travel efficiently through your conveying system. Air leakage causes tiny particles of material to rise into the air or land on surfaces in your facility, creating the potential for major problems like fires and explosions.
Your conveying system needs proper ventilation to prevent these types of air leakage issues. Talk to your valve manufacturer to make sure you have the right airlock for your application, and then replace your rotor when necessary to keep clearances tight.
C is for Combustion
Combustible dust can act as the fuel for an explosion in your plant. The NFPA defines combustible dust as a fine, solid particle that “presents a flash fire hazard or explosion hazard when suspended in the air,” or when it comes in contact with certain concentrations of oxidizing media specific to your process.
When a heat source moves over cold materials (or combustible dusts) and ignites them, it can cause a deflagration in your plant. Deflagration fires generally spread quickly, moving along your line as other hot materials ignite. They can be difficult for fire crews to handle, posing a great risk to your manufacturing plant and your workers’ safety.
A fire can break out in your plant under a combination of specific conditions. The basic formula involves fuel, an oxidizer and an ignition source. In the processing industry, combustible dust is the most likely fuel source. When those three elements come together, they can spark a potentially dangerous fire.
Regular cleaning schedules in your plant, combined with routine maintenance on your valves and other machinery, go a long way towards preventing fires.
H is for Hazard (as in Dust Hazard Analysis)
Dust Hazard Analyses (DHAs) assess the fire and explosion risks of combustible dusts in your plant. According to NFPA 652, they are mandatory for any facility that handles, generates or stores combustible dusts.
There are several different types of DHAs, like the Hazard Operability Analysis (HAZOP) and the Checklist Analysis. The analyses will help you better understand how to mitigate hazards and prevent accidents in your facility.
Ignition is a key ingredient in the recipe for manufacturing plant fires, along with fuel and oxygen. A few different scenarios could lead to ignition:
- Material temperatures on your conveying line rise too high. This can happen with heat-sensitive bulk materials like resins, food powders and sugar.
- Increased rotor speeds or axial shaft movements cause enough friction to spark a fire. Friction can also happen when materials drag or build up.
- If you have a positive-pressure conveying system, compression can elevate the amount of air entering the system, leading to ignition.
To prevent fires, make sure you transport heat-sensitive bulk materials under the correct temperature, humidity and conveying gas conditions. You can also avoid friction by specifying the right types of outboard bearings — ones with temperature switches to detect excessive heat — and shaft seal assemblies, which should reduce heat and static electricity.
The oxidizer is one of the three main elements of a processing plant fire. When a high concentration of oxygen leaks from your system, or when you lack proper ventilation at some point in your conveying line, the presence of fuel and ignition can spark a fire in your plant.
Keep an eye on the ventilation systems in your plant to make sure they’re always functioning at full capacity.
Rotary valves can slow down the spread of flames in your conveying line, as we explain below. To make sure they’re fully functional and NFPA-compliant, you need to regularly check the rotor-to-housing clearances (or tolerances) on your valves. If the clearances rise above 0.0079 inches, you will need to replace your rotor.
Our NFPA Preventative Maintenance Kit includes a replacement rotor and other handy parts to help you stay compliant.
Valves play a critical role in controlling the conditions that lead to fires and explosions in your plant. As isolation devices, rotary valves can stop the spread of flames along your conveying line. They can also regulate fuel and ignition sources to reduce the amount of oxygen feeding a fire.
For optimal fire safety, valves should be properly maintained and equipped with the right features.
Now you know your ABCs. If you have any questions about rotary valve fire safety features or NFPA compliance, contact an ACS Valves representative for more information.