Indicative Monitoring: SKC Haz Dust I vs. Dylos Silica, Volume 1 Episode 6
IM Vol 1, Ep 6
I am going to briefly compare two photometers to make a couple of general points. If I could show you the videos it would be easy to explain and you would get the whole gist. This is not a strict, tightly controlled comparison but it is adequate to make the point.
First let me introduce you to a first generation SKC Haz Dust Model 1100. According to the manual, “HAZ-DUST is calibrated with standard test dust. The particle size range is from 0.1 to 50um this represents the EPA PM10 criteria and thoracic region for airborne particles as defined by the ACGIH (American Conference of Government Industrial Hygienists) and the NIOSH (National Institute of Occupational Health and Safety) Reference method #600.”
I disagree with the contention that the size range identified represents NIOSH 0600 but let’s lay that aside. If the size range of 0.1 to 50um is accurate than the results are more comparable to what you would get with a closed cassette, a total dust sample. I think the manual may have a typo and NIOSH 0500 was intended instead of NIOSH 0600.
The Haz Dust Model 1100 is advertised at the below website for $4,751.00
Second, I re-introduce the Dylos Silica PM2.5/PM10 dust monitor. The Dylos Silica is commercially available but is not advertised at the Dylos website. It will cost about $800.00. This is the monitor I have been using in my respirable silica work. I will not go into detail on correction factors and all that but here are main differences you should know for this article.
1. I did not have a data-logger for the Haz Dust so the data for the graph is taken from videos I recorded of the Haz Dust digital display. The data downloaded from the Dylos is a sample every 15 seconds. The real-time display on the Dylos unit is a rolling average of the last 60 seconds.
2. I hung two Dylos in the stone fabrication shop, the Proto and the Beta. The Beta hung above the Proto with the Proto about 5 feet off the ground. They are in a home-made protective case. There is well defined instrument variability between the Proto and Beta PM10 levels but that is not significant in this example.
3. The only data I use to compare the two is when the Haz Dust was in the same area as the Dylos. I will only use the PM10 concentration from the Dylos.
4. I will make two comparisons. The first is an example of background dust levels when the work crew was on lunch. The second event captured the use of an angle grinder and blade with a make-shift water delivery system that is considered out-dated and not to be used for obvious reasons that you will see.
Background Comparison
This graph and result are not un-expected. The Haz Dust can see a wider range of particles, larger diameter particles than the Dylos can see. We would expect the Haz Dust to read higher because of its ability to count larger sized particles which will also translate to more mass. Now we don’t know the difference in sensing technology in how each device counts particles and we also do not know how the sizing is made and how much mass is assigned to each particle size bin. The density assignment is usually based on the dust used to factory calibrate the monitor. These factors will also contribute to a different result when monitors are reading the same dust sample but again, no surprises here. The background dust levels report a dirtier air space with the Haz Dust than the Dylos.
BLADE CUTTING
The graph below is an approximation of the difference between the two instruments. The cutting was unexpected but it started when the Haz Dust was next to the Dylos. Before I start with the analysis do not pay much attention to the graph after 12:57 as I started to move with the Haz Dust forward towards the misty, dusty plume that has been formed, so the data starts to not reflect measurements of the same air space. Also, at the beginning of the cutting when I noticed the Dylos readings going up, I had to change the concentration range on the Haz Dust from 0-20 mg/m3 to 0-200 mg/m3. What this graph tells me is the dust created by the cutting is largely in the respirable size range and the outputs are fairly the same. Whatever difference of particle size in the shop background is overshadowed by the introduction of massive numbers of particles from the high energy cutting.
The take-home reflects one of the key components I believe that lead to my success with a PM2.5/PM10 monitor and its correlation with NIOSH 0600 integrated samples. If your dust, your environment, your “play-ground”, is largely made up of respirable sized particles with little background dust interference you will get useful real-time data. If background dust is above respirable size it should have little impact but would be better if above PM10. This is partially why I believe water mist from the water controls does not signficantly impact or interfere with the photometer readings assuming the monitor doesn’t get splashed. In large part the water mist and droplets are too big to enter the sensing area and/or be seen. If the source of dust is the process or task you are interested in and there is no competing background dust or other sources of dust fluctuations, you are in a very good place.
Industrial hygienists will understandably have a skeptical eye when being presented with dust monitor data and assertions that the real-time dust levels correlate with concentrations of the dust of interest, but I have seen several advantages with my application, the advantage just described and the additional factor that we only care about the respirable size of silica particles.
This also highlights why an industrial hygienist will be an important asset to assess photometers and their application in a particular environment and to vet claims made by the manufacturer or vendor. Likewise, industrial hygienist have the skills and should use those to explore real-time dust detection systems and not have a knee jerk reaction to the use of these tools as the possibility of dramatically increasing your knowledge and better characterization of exposures and control performance is well worth the work.
dust and mist from the cutting