ISO 23875 FAQ's #1 AND #2

Worldwide implementation of ISO 23875 has produced many questions about various aspects of the standard. The most frequently asked questions will be addressed in a series of posts.

1. What test equipment is required by the standard?

Each of the four tests requires specific test equipment to ensure accurate performance. Prior to conducting the tests, it is assumed that all engineering controls are installed and functioning correctly, as outlined in clause 4 of the standard. Test equipment is required to meet the specifications found in the standard. Test devices by type include:

• Differential pressure monitor

• NDIR CO2 monitor

• Dust monitor

• Fog machine

The devices are included in part in the engineer controls that are permanently mounted in the cab. Below is a further explanation of the devices and how they are used.

1. Pressure Test: The pressure monitor mounted in the cab can be utilized for this test.

2. CO2 Test: The CO2 monitor mounted in the cab can be utilized for this test.

3. Decay Test: To conduct this test, a dust monitor and a fog machine are necessary.

   1. For the dust monitor, it is crucial to ensure that the particulate size range is up to 10 µm. Setting the dust monitor to PM1, or PM2.5 is insufficient; the required size range, commonly referred to as PM10, encompasses the total respirable range of particles.

   2. The fog machine should be a low-wattage model of 400 watts or less, it can be purchased from a party supply store or online retailers such as Amazon or Alibaba. While glycerin-based fog fluids are recommended by the standard, glycol-based fluids can also be used to produce fog for the test with no difference in the test results. Regardless of the fluid type used, a respirator should always be worn when working with respirable particles. Oil based fluids like DOP are not to used in the fog machine. Oil based fluids used for particle generation in the filter testing industry, are not acceptable for use in this testing. These highly respirable oils are toxic .

   3. Recommended dust monitors include the Thermo Scientific pDR 1500 and the TSI Side Pack AM520. Regardless of the make or model, the dust monitor must meet the minimum specifications of the standard.

4. Low-Pressure Leakage Test: This test also utilizes the same fog machine and dust monitor as those used in the decay test.

   1. While glycerin-based fog fluids are recommended by the standard, glycol-based fluids can also be used to produce fog for the test with no difference in the test results.

   2. Regardless of the fluid type used, a respirator should always be worn when working with respirable particles. Oil based fluids like DOP are not to used in the fog machine. Oil based fluids used for particle generation in the filter testing industry, are not acceptable for use in this testing. These highly respirable oils are toxic .

2. What are the particle sizes and volume of fog produced by a low-cost fog machine?

Based on actual readings from the dust monitor, particles exist across the respirable size range, spanning from 0.15 µm to 10 µm. The purpose of the test is to ensure adequate particle volumes across various sizes to assess the air quality system's effectiveness in removing particles from the air. Specifically, the decay test assesses the systems ability to reduce respirable particle concentrations from 2 000 ug/m3 to below 25 µg/m³ within 120 seconds.

In contrast, the low-pressure side leakage test aims to determine whether the system permits a dust concentration exceeding 100 µg/m³ in the cab during testing. The intake filter represents the largest opening in the cab. When connected to an external pressurizer or intake system with the HVAC blower running, particles are drawn toward the intake air filter. If the filter efficiency proves inadequate, the dust concentration in the cab will exceed 100 µg/m³.

To illustrate this, directing particles from the fog machine at a HEPA filter results in minimal or no change in cab dust concentration during the test. Conversely, conducting the same test, for example, with a much lower efficiency filter will result in an interior dust concentration higher than the 100 µg/m³ concentration threshold.

This test effectively identifies instances where dust by-passes the filter, such as low-pressure side leakage in HVAC plumbing, filter seal leakage, or gasket leakages, or when the filter proves inefficient at the 0.3 µm level. The standard recommends that the intake filter be at least 94% efficient at 0.3 µm. While it's feasible to pass the low-pressure side leakage test with a 94% efficient filter, manufacturing variability cannot guarantee this level of efficiency. Hence, it’s best practice to use filters with higher efficiency ratings, such as 97% to 99.99%, to ensure that particles do not ingress through the intake filter in quantities sufficient to fail the low-pressure side leakage test.

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