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
• Oct 15, 2024

The United Kingdom and the United States share many similarities but are distinctly different in the way each nation structures and enforces their respective health and safety legislation, monitoring strategies, sampling methods and limit values.

The UK CoSHH 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 Regulations. Air quality analysis methods are found in the NIOSH manual of analytical methods, which are equivalent to the HSE publication HSG173 and accompanying Methods for the Determination of Hazardous Substances (MDHS) series, while the WELs themselves are published in EH40. 

Both real-time direct reading instruments and personal air sampling pumps are commonly used for workplace exposure monitoring 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 specific 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 certifiable and accurate data that the technique delivers.

The pump is attached to a worker (typically on a belt) with a suitable sampling medium placed in their breathing zone. This could be a filter housed in a sampling head, placed near the workers’ face and run over a sufficiently long time to establish an accurate concentration value which can then be compared with the WEL. Each contaminant will have a dedicated ‘official method’ which will advise on the type of filter and sampling head (or tube for vapors) for the given hazardous substance along with the required flow rate and minimum run time. 

It is vital that the pump has a stable flow rate (and low pulsation) as required by international standard ISO 13137, as the calculated concentration in the case of particulates is directly proportional to the weight of the sample.

Personal Air Sampling Pump – Arguments For: 

• Cost-efficiency: Personal air sampling pumps are generally the most cost-effective in terms of an initial purchase vs a real-time instrument but have ongoing costs with consumables and laboratory 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 standards, giving confidence in the results

• Efficiency: 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 offers a more accurate analysis of airborne contaminant concentration, the samples collected typically require time for the entire process of collection, transportation 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 offer an alternative to this by using advanced techniques such as light scattering to identify the concentration of dust present in the air. Due to the way different dust materials and sizes interact with the light scatter method used, meaning that the analysis can only be considered 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 using 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 control measures.

Real-Time Direct Reading Instruments – Arguments Against: 

• Specificity: Some real-time instruments may lack specificity 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 properly, 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 compared 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 differing particle sizes varies considerably and time should be taken to understand those limitations so that exposure can be accurately assessed.

Controls 

The two countries also align over the use of local exhaust ventilation (LEV) as a common control method. LEV is designed to minimize employee exposure to airborne contaminants in the workplace by capturing the emission at source and transporting it to a safe emission point or to a filter/scrubber. Monitoring systems in appropriate locations, close to these sources or attached to a person close to them, offer employers an understanding of the level of LEV that must be used.

In the US, ventilation regulations are contained as a subpart of the above-mentioned Federal Regulations which reference ANSI design standards. In the UK, best practice is contained within HSG258 and CoSHH Regulation 9 requires testing by a competent person as a legal requirement specifically to examine, maintain and test LEV systems at least every 14 months.

In summary, both real-time direct reading instruments and personal air sampling pumps have their place in workplace monitoring programs in both the U.K. and U.S. Real-time instruments offer immediate feedback and continuous monitoring capabilities but may lack specificity. Personal air sampling pumps provide accurate quantitative data suitable for regulatory compliance but involve delayed results and require more effort in sample collection and analysis. In the US, the choice between the two methods depends on the specific monitoring needs, budget considerations, available resources and local and federal legislations.

This article originally appeared in the October 2024 issue of Occupational Health & Safety.