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.
5. The decay test requires particulate to be injected into the enclosure by placing the fog machine in the enclosure and operating the fog machine by remote control so that the particle density is between 2 000 and 5 000 ug/m3. This is extremely hard to accomplish because the fog machine does not dispense a consistent fog over a 1-2 seconds of time. Additionally, the standard leaves the exact amount of concentration as a range. This appears to be an inconsistent way of doing this portion of the test. How do we reconcile reality with the test requirement?
The intent of the standard is operator protection. The test itself is designed to validate the design and performance of the pressurization system and the recirculation air system in removing particulates from the air inside the cab.
To achieve this goal, particles must be placed inside the cab. This is done inconsistently with a fog machine. The fog particles are effective in simulating dust concentrations in the cab, at issue is the method used to get the particles into the cab at a precise level. Remember the intent of the standard, while recognizing the problems associated with fog machine operation.
After turning on the particle monitor and placing it on the operator seat, turn the machine on, activating the pressurizer, and set the HVAC on low fan speed. Allow the dust concentration in the cab to stabilize and record the stabilized concentration level. Open the door to the cab, turn on the fog machine and allow a short steady stream of fog to enter the cab. Shut the door. The particle monitor that is sitting on the operator seat will indicate the particle concentration. The starting point of the particle concentration must be above 2 000 ug/m3. While monitoring the particle concentration, have a stopwatch, typically found on a modern smart phone, prepared to start timing. When the particle monitor falls to 2 000 ug/m3 start the stopwatch. When the particle concentration falls to 25 ug/m3, stop the timer. The interval on the stopwatch shall be less than 120 seconds to pass the test. If the time is close to 120 seconds, it is recommended to do the test at least two more times to determine that the cab consistently passes the test. If the test is repeated and the system fails to meet the 120 second requirement, the design and potentially the engineering controls may have to be modified to improve system performance.
6. Once the performance tests are completed, assuming they all pass, is the cab certified under ISO 23875?
No, passing performance testing is a requirement of certification but it is only one of many requirements.
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