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. 

Most published LFL values are calculated at room temperature.

However, as a given mixture is heated, its flammability increases and thus the concentration required to achieve 100% LFL is less. This source of increased danger is often overlooked.

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.

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.

Industrial fires and explosions happen more frequently than most people think. They cause downtime, property damage, injury and sometimes death. These fires and explosions result from a dangerous mixture of flammable vapors with air and a source of ignition.

For the past month we shined the spotlight on process ovens & dryers; we've looked at WHAT goes on in the application, WHICH hazards to avoid and WHY they should be monitored.

Controlling flammable vapors and installing solvent vapor monitors on your process oven and dryers allows the implementation of several money-saving steps:

Moving and heating large amounts of air can be extremely expensive. Many manufacturing processes must use chemical solvents in the production of their products. As a result, hot air dryers are frequently used as a means of evaporating those solvents.

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.

Experience has shown that explosions in ovens and dryers can happen very quickly. The key hazard is an explosion from the build up of solvent vapors in the oven or dryer atmosphere. This buildup could occur by a malfunction in the production process such as:

• a sudden or improper amount of coating 
• a change in ventilation controls 
• excessive speed

In any of these cases, the concentration of flammable vapor has an opportunity to rise above safe levels, creating a potentially explosive mixture of vapor in air.