Effective hazard monitoring in grain environments is something that’s easy to take for granted. Yet, despite a long-term decline in explosions, injuries, and deaths, we still see about seven grain elevator explosions a year. In fact, there was a recent explosion in Omaha a few months ago that may have been caused by a grain dust explosion in which 10 people were hospitalized and two people were killed. It really goes without saying that it’s worth periodically taking a closer look at current standards and best practices around hazard monitoring.
I had the opportunity to present some of these in detail at the most recent GEAPS Exchange Conference in Omaha, and I’d like to explore portions of that presentation here on our Lakeland Labs blog over the course of a few posts, so keep coming back!
To begin with, an explosion requires three simple things: fuel, oxygen and ignition. The fuel in a grain elevator is inevitably grain dust. Ignition can be created by sparks or simply by high temperatures. This situation can be particularly nasty because dust particles have a lot of surface area surrounded by oxygen. I’ve embedded a video here to give you a look at what this looks like in a lab setting with corn starch.
Let’s take a closer look at ignition caused by high temperatures. There are three causes I’d like to particularly call out: belt slippage, belts out of alignment that run up against equipment, and bearing temperatures. Friction is our enemy here but we can use monitoring to address each.
In the case of belt slippages, we’ve had belt alignment switches in place for many years, and if a belt starts to track from side to side, it puts pressure on the switch that either triggers an alarm or shuts it down. OSHA requirements dictate that if slippage of the belt causes operating speed to drop to 80 percent of normal, the system must automatically shut down. That’s the legal requirement. Many places have chosen to set that at 90 percent to provide an extra margin of safety.
Rub blocks are often put in place to detect alignment issues. Essentially, they’re set in place so that if a belt begins going out of alignment, they simply touch the rub block and transfer friction heat to a central control system through a heat sensor. The rub blocks are typically made of brass because it transfers heat so well. The control system can then provide an alarm or the system can shut down. A word of caution here: Sometimes you will see rub blocks mounted improperly such that the belt hits the equipment first, which defeats the whole purpose!
Finally, bearings can get hot enough to trigger an explosion too, so we install bearing sensors that can detect temperatures close to the bearings and send that information to the control system.
In upcoming posts we’ll take a closer look at thermocouple sensors, analog multiplexors, digital sensors and more.