Building Lines of Defense Against Hydrocarbon Releases and Fires

 In a Chemical Engineering article, Emerson’s Nick Pinto offers strategies for improving tank farm safety with more effective gas release and flame detection

In countless war movies, the heroes, whether in trenches or spaceships, have to stop the enemy advance at some particular point, providing the last line of defense to avoid disaster.

This may be overly dramatic, but designing an overall safety strategy for large-scale flammable liquid storage systems must consider multiple lines of defense, and how an incident can punch through them one by one if not impeded. A design team should analyze all the steps that might ultimately lead to a catastrophic fire and explosion, and how appropriate detectors can stop the advance.

That’s the topic of my article in Chemical Engineering. The first line of defense is always an effective process control system combined with a safety instrumented system, working together to keep flammable liquids and gases safely stored in the proper tanks. These should work automatically, virtually all the time. But things can go wrong, and when they do, an effective and proportional response is required.

If the situation is beyond what the SIS can deal with, a release of flammable liquid or gas might occur. Gas systems might also contain toxic gases, such as hydrogen sulfide, but for finished products, these have likely been removed already. Flammability is the more immediate concern. Gasoline spilling onto the ground becomes vapor and escaping propane is gaseous. Gas detectors look for these and other hazardous gases, hopefully before each finds an ignition source, and reports results. If fires do break out, flame detectors respond as quickly as possible so alarms can be activated, and so suppression systems can act appropriately.

So, the situations we’re concerned with here are after the first lines have failed, allowing liquids and gases to escape their normal containment—gasoline is running onto the ground, or a plume of propane is shooting into the air. How do we know those things are happening, and worse, how do we know when a fire has started?

We can “hear” a compressed gas, like propane, escaping by using Emerson’s Incus Ultrasonic Gas Leak Detector with its ultra-sensitive acoustic sensors.

We can “smell” a flammable gas or vapor by using Emerson’s Net Safety Millennium II SC310 Catalytic Bead Combustible Gas Sensor, which works with all flammable gas types and delivers % LEL detection quickly and reliably.

We can “see” a flammable gas by using Emerson’s Rosemount Open Path Gas detectors, which respond to critical wavelengths of light absorbed by hydrocarbon vapors.

If a fire actually breaks out, Emerson’s Rosemount 975MR Multi-Spectrum Infrared Flame Detector accurately captures and analyzes the multi-spectral signals produced by flames, even at long distances.

All these tools can work together to shore up critical lines of defense for any storage facility. What’s the situation where in your plant or facility? Are there enough detectors to allow your remediation actions to be proportional to the hazard, but still effective?

Visit the Flame and Gas Detection pages at for more on technologies and solutions for flammable gases and fires. You can also connect and interact with other engineers in the Chemical and Oil & Gas Groups at the Emerson Exchange 365 community.

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