We've discussed the 6 essentials of meeting NFPA 86, this week let's take a closer look at the fourth monitoring requirement: avoiding condensation.

NFPA 86 Section 11.6.10.11 requires that “the sensor and sample system shall be maintained at a temperature that prevents condensation.”

Condensation of any part of the vaporized sample will create two types of problems:

  1. If any flammable vapors condense, the readings will be lower than actual (unsafe error). 
  2. Any condensation will produce sample line clogging and fouling, resulting in higher maintenance and system downtime.

Condensation can be avoided by heating the entire sample line and sensor assembly above the condensation temperature of the sample. It is very important to consider not only solvents, but all constituents of the sample, including resins, plasticizers, and other high- molecular-weight compounds present in the sample. In some cases, the temperature required to avoid condensation is above the operating temperature of available heat- traced sample tubing. In these cases, the sensor must be mounted directly onto the process ductwork, with no external sample line.

It is also important to note that sample conditioning (chiller) systems cannot be used in LFL monitoring because they condense flammable vapors, which results in false low readings.

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