Page 44 - OHS, October 2024

I H I N S T R U M E N T S / M O N I T O R I N G
Real Time vs. Personal Air Sampling Instruments: You Decide
Weighing the pros and cons of the two major types of air quality analysis.
BY TIM TURNEY
similarities but are distinctly diff erent in the way each na-
The United Kingdom and the United States share many
tion structures and enforces their respective health and
safety legislation, monitoring strategies, sampling meth-
ods and limit values.
Th e UK CoSHH1 Regulations are quite clear when it comes to
the need to monitor for airborne hazards:
■ To show compliance with a workplace exposure limit (WEL).
■ When you must show that control equipment is working.
In the US, both guidelines and exposure limits are embodied
in the relevant parts of the same Federal Regulations2. Air qual-
ity analysis methods are found in the NIOSH manual of ana-
lytical methods3, which are equivalent to the HSE publication
HSG1734and accompanying Methods for the Determination of
Hazardous Substances (MDHS) series5, while the WELs them-
selves are published in EH406
.
Both real-time direct reading instruments and personal air
sampling pumps are commonly used for workplace exposure mon-
itoring to assess potential hazards to workers’ health. Each method
has its advantages and limitations, and the choice between them
depends on various factors such as the specifi c contaminants being
monitored, the nature of the workplace environment, the desired
level of accuracy, and the resources available.
Air Sampling Pumps
When it comes to compliance, both the US and the UK employ air
sampling pumps as the standard measure. Both the HSE and the
relevant Federal Regulations use air sampling pumps because of
the certifi able and accurate data that the technique delivers.
Th e pump is attached to a worker (typically on a belt) with a
suitable sampling medium placed in their breathing zone. Th is
could be a fi lter housed in a sampling head, placed near the work-
ers’ face and run over a suffi ciently long time to establish an ac-
curate concentration value which can then be compared with the
WEL. Each contaminant will have a dedicated ‘offi cial method’
which will advise on the type of fi lter and sampling head (or tube
for vapors) for the given hazardous substance along with the re-
quired fl ow rate and minimum run time.
It is vital that the pump has a stable fl ow rate (and low pul-
sation) as required by international standard ISO 131377, as the
calculated concentration in the case of particulates is directly pro-
portional to the weight of the sample.
Personal Air Sampling Pump – Arguments For:
■ Cost-effi ciency: Personal air sampling pumps are generally
the most cost-eff ective in terms of an initial purchase vs a real-time
instrument but have ongoing costs with consumables and labora-
tory analysis.
■ Sensitivity: Highly sensitive techniques used by personal
air sampling pumps can ensure more accurate results required to
comply with occupational exposure limits and regulatory stan-
dards, giving confi dence in the results
■ Effi ciency: Personal pumps allow for samples to be collected
over a working day. As the concentration of particulates can be
calculated using a time-weighted average.
Personal Air Sampling Pumps: Arguments Against:
■ Time: While laboratory testing off ers a more accurate analy-
sis of airborne contaminant concentration, the samples collected
typically require time for the entire process of collection, transpor-
tation to the lab and the testing which leads to delayed results.
■ An average only: Air sampling provides an accurate level of
exposure against a reference method, but only an average level for
the day. It cannot say when or where the exposure came from. For
example, a high average result could come from a very high peak
at a single time or an elevated consistent high level during the day.
■ Specialization: Personal sampling pumps require a certain
amount of training and expertise to ensure the correct setup and
selection of the correct collection media.
Real-Time Direct Reading Instruments
With technological advancements, real-time instruments off er an
alternative to this by using advanced techniques such as light scat-
tering to identify the concentration of dust present in the air. Due
to the way diff erent dust materials and sizes interact with the light
scatter method used, meaning that the analysis can only be con-
sidered as indicative and a method for implementing controls to
reduce the risk. For compliance, both the UK and the US insist on
the use of air sampling pumps.
Real-Time Direct Reading Instruments – Arguments For:
■ Instant Feedback: Real-time instruments provide instant,
continuous measurements, allowing for immediate feedback on
exposure levels rather than waiting for laboratory results when us-
ing an air sampling pump.
■ Not the average: Real time instruments can log the time
history of exposure levels, providing the ’when’ of an exposure
event, which makes it easier to identify what to prioritize for con-
trol measures.
Real-Time Direct Reading Instruments – Arguments Against:
■ Specifi city: Some real-time instruments may lack specifi city
and sensitivity for certain contaminants compared to laboratory
analysis and can also faulter in accuracy if not calibrated properly.
■ Maintenance: Similarly, if the units are not maintained prop-
erly, they will begin to return inaccurate or even incorrect results.
■ Cost: With cost being on the agenda for any purchasing
manager, real-time instruments can be relatively expensive com-
pared to personal air sampling pumps, especially high-end models.
■ Training: Interpretation of real-time data may also require
specialized training to understand factors such as instrument
limitations, interferences, and environmental variability. Although
many instruments use similar light scatter methods, their response
and ability to detect diff ering particle sizes varies considerably and
time should be taken to understand those limitations so that expo-
sure can be accurately assessed.
44 Occupational Health & Safety | OCTOBER 2024 www.ohsonline.com