I often receive e-mails with questions about filter or filtration system capability. Below is a typical example from a machine bid specification it exhibits a major problem prevalent across the heavy equipment industry; many folks who should know something about cabin air quality actually know very little!
Customers tend to request a very specific filter rating, which is often HEPA. An authentic High Efficiency Particulate Air (HEPA) filter is a minimum 99.97% efficient at 0.3 microns. In many applications, HEPA filters are not necessary to achieve minimum threshold dust levels as described in ISO 23875 amendment 1. Furthermore, they are more costly and, generally, have less filter life than alternative Efficient Particulate Air (EPA) Filters, which are between 95 and 99% efficient at 0.3 microns. Specifying HEPA filters does not guarantee a safe level of air quality for the operator in a machine cab. Other factors contribute to the overall system that protects the operator. These factors include the amount of fresh air drawn into the cab, cab pressurization, air exchanges through the recirculation filter within the cab, and the ability to monitor cab pressure and CO2.
The question people should be asking is what level of operator protection can be provided by the cab air quality system? ISO 23875 with Amendment 1 is important because it is focused solely on operator air quality as defined by two primary contaminants: respirable dust and CO2. As a life cycle standard, ISO 23875 with Amendment 1 is a road map that, when followed, provides compliant air quality for the life of the machine. If compliance with a silica regulation is required, ISO 23875 with Amendment 1 provides the path to compliance. Because of this, the operator enclosure section of mining machine tenders should require ISO 23875 with Amendment 1 as the specification.
It is not uncommon for the bid spec to state “filters must be rated as ISO 15E (or MERV16) yet tested per ISO 29463” There are a number of issues blended together in this simple statement. The MERV rating for air filters comes from ASHRAE Filtration testing standard 52.2, which is completely different from ISO 29463. The MERV 16 filters are tested for average efficiency between 0.3 microns and 1.0 microns. The ISO 15E-rated filter is tested at the most penetrating particle size (MPPS). The ISO 29463 test method and the ASHRAE 52.2 test method are radically different, and filters rated under either test method have no correlation to each other. This specification request is impossible to reconcile and has to be sent back to the customer for clarification. The customer who wrote the bid is rarely able to provide an answer because of the difficulty in contrasting the two different test methods and filter rating systems. The customer should stop trying to engineer a filtration solution and instead specify ISO 23875 with Amendment 1 in their request. This would allow the machine manufacturer to apply ISO 23875 with Amendment 1 and deliver a cab that provides compliant air quality.
In conclusion, The International Society of Environmental Enclosure Engineers (ISEEE.NET) provides specific online education available 24/7 for engineers, occupational hygienists, cab engineers, filtration engineers, retrofitters, HVAC engineers, and any other stakeholders seeking to understand ISO 23875 with Amendment 1. If you are responsible for writing machine tenders, you owe it to your company and your operators to implement ISO 23875 with Amendment 1 in our machine specifications. This one addition will make it possible for your company stakeholders to get what they desperately need, cabs that provide compliant air quality.