Particulate monitors: Expectations vs. Reality

Jun 27, 2019 3:00:00 PM

Particulate monitors: Expectations vs. Reality

With 12,000 people dying every year in the UK from past exposure to harmful dust particulates in the workplace, the time has come for particulate monitors to evolve and protect the workers who run the risk of illness in the future.

The generation of hazardous dust has always been an inherent part of some industrial processes, be they textile weaving, mining, food production, household pharmaceuticals, large project construction or heavy manufacturing.

However, international legal action and high-profile court cases involving asbestosis, black-lung and silicosis, which frequently result in fines and compensation claims running into the hundreds of millions of pounds, have projected the harmful effects of dust into the public eye.


The limitations of existing particulate monitoring technology

Industries that have by their very nature been most closely associated with the generation of hazardous particulates have taken heed of the potential financial penalties and reputational damage that can follow such legal action.

As a result, they have encouraged and embraced the whole science of dust management, from the prevention and containment of dust through to stopping the release of airborne particulate matter into the immediate environment.

Preventative methods usually involve multiple different approaches including: engineering out dust emissions; protecting workers by employing appropriate personal protection equipment (PPE) (goggles, gloves, face masks, dust helmets etc.); ventilation management; dust capture; and dust suppression.

These preventive methods only form part of the solution to providing operatives with a safe working environment, and particulate exposure will always be an issue wherever material movement, storage, manufacturing and processing occurs.

To efficiently and proactively counter the wider issue of airborne particulate matter, the problem must first be accurately located and identified. The issue of worker exposure can only be properly tackled when temporal trends and patterns related to particulate matter exposure are identifiable. Current methods of particulate monitoring are not best suited to solving this problem as they are unable to characterise the particulate matter (concentration, size and shape distributions and chemical composition), in real-time with configurable, accurate metrics.

During the development of identification and monitoring techniques, two methods have emerged to become commonly used in hazardous environments.

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The gravimetric method

Using this method, filter paper is weighed and placed within a filtration unit which sucks or pumps air through and “catches” particles in the filter. After a pre-determined period of time the filter paper is removed and weighed again with the difference in weight used to determine the levels of particles within the environment.

This technique, however, has a number of inherent limitations.

  • The filter paper deployed within the devices can only be used to measure one size profile at a time. Additional size filtration and selection is provided by physical aerodynamical prefilters.
  • A device will prefilter out particulates larger than a particulate PM size – be it 10, 4.25 or 2.5.
  • The particulates which then reach the filtration paper will be caught by the filter paper with a probability that relates to the individual particulate size and filter paper type.
  • This produces an artificial distribution of particulate matter that is contained within the air and is a physical limitation of the hardware in use.
  • The form of the distribution is hard to change and does not necessary match or represent what would be the optical measurement distribution.
  • What you get is a reference against an industry benchmark standard for particle measurement with an accuracy range of +/- 25%.
  • The measurement – while technically continuous – doesn’t provide a real-time picture.
  • There is no temporal resolution and only one data point is obtainable - for instance it is not possible to distinguish between an area with a generally high background level and an area with a low background level that contained a relatively high spike.
  • This monitoring method is also taken as a representative sample, meaning if anything in the process or environment changes the readings will no longer represent the environment and therefore not be valid.

Finally, because the real analysis of the particles only happens once the filter paper has been removed and the particles analysed in a laboratory (which can take days or even weeks), by the time the level and nature of the particulates have been identified, operatives have likely already been exposed for some time – meaning any new controls implemented are late and feasibly ineffective due to subsequent environmental changes.


Light scattering technology in the form of a nephelometer

Nephelometers measure particulates by using a light beam and a light detector, often set to 90 degrees of each other. As particulates pass through the light beam, particulate density is measured by the light reflected into the detector.

Whilst this method provides more accurate measurement of particulates in the atmosphere, it still encounters a number of limitations.

  • The most basic optical particle counters still don’t have the ability to count individual particle sizes and can only offer a rough concentration measurement of what is in the atmosphere.
  • Other particle counters are able to measure individual flashes of particles moving through the beams, but don’t have the profiling capability to capture individual particulate sizes.
  • This allows for a single concentration of a standard size distribution to be obtained.
  • Like the filtration method, these particle counters are reliant on pumps and filters to draw the particles into the monitor.

These devices, whilst producing a real-time data-set, are unable to record data with a temporal resolution high enough to identify trends and patterns with particulate matter concentrations recorded once every 30 minutes to 1 hour. Data produced with a low temporal resolution such as this makes it hard to identify the causes of potential problems and can often act to blur or hide trends that would have otherwise been noticeable.


The problem with current technology

One of the major problems with both the gravimetric and light scattering methods of measurement in current particulate monitors is that both devices rely on moving parts such as pumps or filters to control the airflow into the device. This isn’t a problem when being tested in lab conditions, but when these monitors are used in the dirty and harsh environments they are meant for, they are highly susceptible to malfunction by becoming clogged with a buildup of dust and dirt.

Ultimately they are not robust enough to perform for a sustained period of time in harsh environments, making them unreliable.


The next generation of laser technology

One of the biggest advancements to the field of particulate monitoring is the introduction of high quality and practically obtainable laser technology. The introduction of this technology has enabled devices and techniques, only previously available in high-end, delicate and expensive laboratory instruments, to be used and developed for harsh industrial environments.

Much like the development of battery technology, which has reached the point where the advances made at the top end of the technology has meant that we can power cars for hundreds of miles and carry small computers in our pockets, the development of laser technology is now able to greatly benefit the particulate monitoring industry.

The latest generation of laser technology allows for optical particle sizing, meaning that as a particle passes through a unit, it is not only  counted, but the size of that individual particle is measured as well.

These advancements are finally presenting the opportunity for units that can produce an accurate, continuous and real-time overview of particulate activity within harsh and hazardous environments.


Accurate, real-time AND continuous

The Air XD Real-Time Dust Monitor is bringing accurate, real-time and continuous monitoring to harsh and hazardous environments for the first time. By combining next generation laser technology with a custom algorithm to provide a dynamic sizing capability, the Air XD system can provide particulate size profiling across an entire operation.

Unlike standard devices which can provide a PM value and rough concentration level every pre-determined time period (i.e. every hour), the Air XD particulate monitor has the capability of monitoring up to 10,000 particles a second. Every particle that is measured is “binned” into one of 20 size bins, these bins are then collated every 10 seconds and a concentration for each size bin calculated. Any size profile, either an industry standard such as PM 4.25 or PM 10, or a custom size profile suited to a specific process can then be calculated, with a time resolution of 10 seconds.

By accurately recording the amount and size of particles that pass through the laser contained within the unit, businesses and/or environment safety officers are able to employ a full spectrum monitoring capability. This allow trends in concentration levels to be identified and then reaction or adjustments to made instantly – this adds a new level of protection to operatives.

The Air XD also benefits from having no moving parts – no pumps or filters – meaning it is far more reliable than any of the current monitors available and delivers lab-grade monitoring accuracy contained within a unit which meets ATEX standards of robustness and reliability within harsh and hazardous environments. Each particle that passes through the laser beam has its time-of-flight measured and recorded, removing the assumption that the air-flow is fixed and continuous; this removes the danger of under- or over-sampling.


Particulate Monitoring eBook

If you're interested in finding out more about particulate monitoring within harsh and hazardous environments, why not download our eBook?






Written by Trolex News