The Safety and Performance of your Printing Line: Sensor Choices and How to Decide

Although several different types of sensors are employed as LFL monitors, each has an appropriate application to which it is best suited.

Fires and explosions in what was thought to be “protected” equipment can occur without warning when a sensor is not capable of doing the job that had been assigned to it.

This is most often caused by a misunderstanding of the different available technologies.

The Safety and Performance of your Printing Line: Application Examples

Typical Flexographic Application Examples Include:

  • Drying systems for printing lines
  • Abatement systems such as oxidizers

Processes that use flammable solvents can develop explosive concentrations due to failure of coating, metering, ventilation or heating systems, adverse chemical reactions, and human error.

LFL monitors are used for safety as well as process efficiency, protecting the system from fire and explosion while also allowing operating at higher vapor concentrations to save costs.

The Safety and Performance of your Printing Line: Response Accuracy

There are important considerations when choosing an LFL monitor:

  • Response Accuracy
  • Response Speed
  • Condensation Issues
  • Failsafe

First let's look at response accuracy.

There are several technologies used to measure flammability, and few react the same way to all substances. 

A sensor or analyzer calibrated to accurately read one substance may be significantly inaccurate for another process component. This variance from perfect accuracy (error) is known as the Response Factor. 

The Safety & Performance of your Printing Line: Safety Margins

Almost all safety authorities require a 4:1 margin of safety below the LFL, based on worst-case conditions. This means that enough dilution air must be used to always maintain a concentration of less than 25% of the LFL, according to the National Fire Protection Association standard NFPA 86.

The Safety & Performance of your Printing Line: Basics of Flammability Measurement

For each flammable substance there is a level of concentration in air, usually expressed as a percent by volume, that is known as its Lower Flammable Limit, LFL, or Lower Explosive Limit, LEL. Below the LFL, the mixture of fuel and air is too lean to support combustion. For example, a mixture of 1.1 percent Hexane in air is equal to 100% of its LFL - just rich enough to propagate a flame.