NFPA 25 – 水基消防系统检查、测试和维护标准，2014 年版，建议每年对泡沫系统进行流动，并对泡沫溶液进行测试以验证浓度。此外，NFPA 11 – 低、中、高膨胀泡沫标准，2010 年版在第 11.6.4 节中推荐以下内容 – “泡沫浓度应具有以下比例之一：1）不低于额定浓度和2) 不超过额定浓度的 30% 或高于额定浓度的 1 个百分点（以较小者为准）。 NFPA 11 附件 B 认可了三种确定泡沫溶液浓度的方法。可以使用折光仪或电导仪分析泡沫溶液。或者，可以通过测量水和泡沫溶液的流速来确定浓度。 为了使用折射率或电导率计算泡沫溶液的浓度，将泡沫和水以已知浓度混合，并将已知溶液的折射率或电导率与未知系统溶液进行比较。为确保准确性，应考虑以下事项： * 标准溶液必须准确混合。 * 用于混合标准溶液的水必须代表泡沫配比系统中使用的水。这在使用电导率方法时尤为重要，因为水的电导率可能会发生显着变化。 * 用于混合标准溶液的泡沫浓缩液必须代表泡沫配比系统中使用的泡沫浓缩液。请记住，不同品牌泡沫浓缩液的折射率和电导率可能会有很大差异，并且同一品牌浓缩液的批次之间也可能有显着差异。 * 折射计或电导率计必须提供准确的值，并且必须考虑温度等变量。 * 系统解决方案必须以模拟火灾情况下的流量的流量生成。
Verifying that a firefighting foam system accurately proportions foam and water is critical to the system’s effectiveness in the event of a fire. If the premix solution is mixed too lean—not enough foam concentrate and too much water—it may not be able to extinguish the fire. If the premix solution is mixed too rich—too much foam concentrate and not enough water— there is a risk running out of foam before the fire is fully extinguished.
NFPA 25 – Standard for the Inspection, Testing and Maintenance of Water-Based Fire Protection Systems, 2014 Edition, recommends that foam systems be flowed annually and that the foam solution be tested to verify the concentration. Furthermore, NFPA 11 – Standard for Low-, Medium-, and High-Expansion Foam, 2010 Edition recommends the following in Section 11.6.4 – “Foam concentration shall have one of the following proportions: 1) not less than the rated concentration and 2) no more than 30 percent above the rated concentrate or 1 percentage point above the rated concentration (which-ever is less).” NFPA 11, Annex B recognizes three methods for determining the concentration of a foam solution. The foam solution can be analyzed using a refractometer or a conductivity meter. Alternatively, the concentration can be determined by measuring the flow rates of both the water and the foam solution.
In order to calculate the concentration of the foam solution using either refractive index or conductivity, foam and water are mixed at known concentrations and the refractive index or conductivity of the known solutions are compared to the unknown system solution. In order to ensure accuracy, the following items should be considered:
·The standard solutions must be mixed accurately.
·The water used to mix the standard solutions must be representative of the water used in the foam proportioning system. This is particularly important when using the conductivity method as the conductivity of the water can vary significantly.
·The foam concentrate used to mix the standard solutions must be representative of the foam concentrate used in the foam proportioning system. Keep in mind both the refractive index and conductivity of different brands of foam concentrate can vary significantly and can also vary significantly from lot to lot of the same brand of concentrate.
·The refractometer or conductivity meter must provide an accurate value and variables such as temperature must be taken into account.
·The system solution must be generated at the flowrates that mimic the flows in a fire situation.