Back to the Basics: Minimum Ventilation Rate

There are several fundamental safety precautions which should be applied to all dryer designs.

These requirements call for a minimum below which the ventilation rate is never reduced. This predetermined, fixed value is calculated from solvent input and flammability characteristics. Fundamental safety does not require use of an analyzer but, if none is used, the LFL limit is usually decreased to about one half the value allowed when an analyzer is installed.

Back to the Basics: Transient conditions

Last week we discussed the first type of process upset that could present a hazardous condition, the steady-state, this week let's focus on on the condition that poses the greatest difficulties in detection and correction.

Process upsets from transient conditions produce a hazard from an unstable process that is changing relatively quickly. Causes include: 

Back to the Basics: The Steady State

In order to determine the suitability of a particular analyzer system, it is useful to study potential process upsets. 

There are two main types of process upsets that could present a hazardous condition: 

  1. The steady-state (approximately time invariant) 
  2. The transient (time sensitive)

Of these, the transient upset condition poses the greatest difficulties in detection and correction. But before we get to that let's look at the steady-state conditions:

Back to the Basics: Safe reduction of ventilation

Last week we discussed the 2 cases at which the authorities have determined that certain industrial processes can proceed at solvent vapor concentrations up to, but not exceeding, some percentage of the Lower Flammable Limit.

Let’s focus on case #2: What happens when an analyzer and control system are used? 

Back to the Basics: Limits to solvent vapor concentration

The authorities have determined that certain industrial processes can proceed at solvent vapor concentrations up to, but not exceeding, some percentage of the Lower Flammable Limit. 

In general, there are two cases:

  1. The fundamental safety limit
  2. The limit when an analyzer and control system are used

This week let's take a look & expand upon Case #1: Fundamental ventilation requirements.

Back to the Basics: Temperature Effects on LFL

So we know what the LFL is and how it's determined, but what about the factors that can effect these values?

Back to the Basics: Variation in Published LFL Values

Now that we understand what the Lower Flammable Limit is, let's look at how these values are determined and what that means for your application. 

LFL is determined empirically. This means that there are variations in the values published by different authorities at different times. 

It is likely that the following test conditions account for the deviations in these published values:

Back to the Basics: LFL

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.

There are 3 important factors to consider when measuring flammability: 

Back to the Basics: Flammable Hazards

The next topic in our "back to the basics" series is flammable hazards. Its important to understand what causes a fire or explosion to occur in a process before you can even think about preventing one.

Back to the Basics: The Role Of The Analyzer

Hello 2016.

The clean slate of the new year makes it the ideal time to make a firm decision to facilitate improvement in some area of your life or business.

Many businesses make resolutions, but when they don’t work, it’s often because the goals are impossible to achieve, the fixes that are needed can’t happen in a short time, or there are simply too many. Because the success rate for resolutions is so low, it would be wise to continually review your goals, examine what has brought success, and go back to the basics.

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