by Grant Lobdell
According to the current, 2018 edition of National Fire Protection Association (NFPA) 10 Standard for Portable Fire Extinguishers, prior to reuse, dry chemical shall be thoroughly checked for proper type, contamination, and condition (7.8.3.4.2). Dry chemical found to be the wrong type or contaminated cannot be reused (7.8.3.3.2).
Due to the limitations of visual inspections, Dyne Fire Protection Labs offers a thorough chemical analysis to fulfill these requirements. This analysis currently involves verifying the concentration (% by mass) of the following:
Contamination
· Moisture
Formulation
· Ammonium Sulfate
· Calcium Carbonate
· Monoammonium Phosphate
· Potassium Bicarbonate
· Potassium Sulfate
· Sodium Bicarbonate
· Sodium Chloride
Moisture Analysis
Dyne Fire Protection Labs determines moisture in a dry chemical sample by Karl Fischer Titration. Moisture is driven out of the sample and into a reagent that is monitored for any electrical changes resulting from the water. The advantage of this analysis over the more common loss-on-drying technique is that the analysis can be done much quicker and with less hassle while still maintaining or exceeding the accuracy and repeatability of previous techniques.
The 2018 edition of ISO 7202 Fire protection – Fire extinguishing media – Powder, section 10, states that the moisture content of a dry chemical agent should be <0.25%. A sample with high moisture content is subject to caking which will impact the dry chemical’s ability to flow through the equipment as designed.
Chemical Composition Analysis
Dyne Fire Protection Labs determines the chemical composition of a dry chemical sample by ion chromatography. The sample is diluted with water and the resulting solution is run through a column designed to separate any ions in solution. As the ions of interest come off the column, they are quantified by monitoring electrical changes. Given the concentration of each ion in the sample, Dyne Fire Protection Labs can calculate the concentration of each target compound. Based on the determined formulation, Dyne Fire Protection Labs can determine the type of agent.
The concentration of each target compound is compared to manufacturer specifications. According to the 2018 edition of ISO 7202 Fire protection – Fire extinguishing media – Powder, section 5.4, a dry chemical agent must be within ±1% (for components designed to be between 10-15%), ±1.5% (for components designed to be between 15-25%), ±2% (for components designed to be between 25-65%), or ±3% (for components designed to be above 65%) of the manufacturer declared concentration. A sample found to not be within the tolerances allowed by these specifications would not be of equal chemical composition to the agent listed with the equipment as required by 7.8.3.1 of the 2018 edition of NFPA 10. Agents of the correct type but of differing chemical composition from the equipment listing have not been evaluated with such equipment and therefore may not perform. Agents of the wrong type will not work on the intended hazard.
If you have any questions regarding this article, please contact Dyne Fire Protection Labs at lab@dyneusa.com or (800) 632-2304.
©Dyne Fire Protection Labs 2020