There are different types of dust sampling methods – high volume, low volume, optical, beta attenuation – and there are different levels of certification too. We always get asked – how does this equipment compare to that equipment? What does equivalent mean and how does that compare to reference? We wrote this blog to explain, hopefully it helps.

For the purposes of comparison, we put popular dust monitoring instruments into four different performance classes: certified reference, certified equivalent, certified indicative, and indicative. The terminology is based on terminology that is commonly used in the United States and Europe.

The main difference between instruments from the different classes is the cost (purchase, and operational cost) and accuracy. Generally speaking the higher the accuracy the higher the cost.

The diagram below gives a quick visual of the different types of environmental dust monitors on the market including our own Dust Sentry and Dust Profiler instruments.

The two instruments shown in the Certified Reference class are the high volume sampler and the Partisol. There are many other instruments which have reference certification, but these are the most common.

To be classed as Reference, instruments must employ the gravimetric method of particle measurement. A gravimetric method is a quantitative measure based on the mass of the solid.

Although this is the most accurate method of particle measurement it has three big disadvantages compared to methods from other classes.

In summary, reference instruments are very accurate but they are expensive to operate and can’t provide an hour by hour view of environmental dust levels.

Equivalent methods are so called because they have been shown to have performance that is equivalent to Certified Reference instruments. That does not mean they perform exactly the same, but they do meet some objective pass/fail criteria set by the US EPA, MCERTS, TUV or similar regulatory body.  

The three instruments shown in the Certified Equivalence class are the TEOM from Thermo Fisher Scientific, the BAM from Met One, and the EDM 180 from Grimm. There are many other instruments which have indicative certification, but these are the most common.

Several different measurement methods have been certified as equivalent. Each method has unique challenges and sources of error. All instruments in this class are more expensive than instruments in the Certified Indicative class. They can also be more expensive than instruments in the Certified Reference class.

Equivalence methods have two main advantages compared to reference methods:

The equivalence methods have some disadvantages:

In summary, Certified Equivalent instruments are accurate and provide hour by hour data, but the total installation cost can be high, and they cannot provide minute by minute data.

Indicative means that the data has been shown to be indicative relative to Certified Equivalent instruments. Indicative is a term used more often in Europe where there is a formal definition of the criteria for Indicative instruments. The formal criteria led to the creation of the world’s only standard for indicative dust monitoring instruments, MCERTS.

Several manufacturers (including Aeroqual) have been able to demonstrate performance to meet MCERTS standard for indicative dust monitoring. The standard requires a full 40 day field trial of two indicative dust monitors against two reference or equivalent dust monitoring instruments. In addition the manufacturer must pass a factory inspection to ensure that quality systems are in place that will ensure instruments are produced of a consistent high quality.

There are many environmental dust monitors on the market which do not have any performance certification. They include the TSI DustTrak and the Dust Guardian from Casella.

Certified Indicative instruments have several advantages compared to Certified Equivalence instruments:

One disadvantage of Indicative instruments is that they may need calibration against a Reference instrument. It isn’t always required but if it is, it adds cost to the initial commissioning of the instrument.

In summary Certified Indicative instruments have significant cost advantages. They are affordable and easy to use. Certified instruments have been shown to meet formal accuracy and quality standards. Finally, servicing requirements can be lower and that keeps the total cost of ownership down.

It depends on your application and budget. For an affordable and reasonably accurate environmental dust monitor then a Certified Indicative instrument is a good choice. Where high accuracy is required and cost is not a barrier then you should consider a Certified Reference or Certified Equivalent instrument. If daily data is enough then Certified Reference might be right for you. If you need minute by minute data then you must have an Indicative monitor.

In many cases a mix of instruments can offer the best of both worlds. This blog post talks about the merits of mixing Reference with Indicative instruments in construction and mining applications. The Reference instrument gives highly accurate daily readings; the Indicative instrument gives minute by minute data that can be checked against the Reference data to ensure traceability.

If you still need help choosing, talk to a professional. Like us – we’re always happy to help!