Something in the air
01 December 2021
Tim Turney shares best practice advice on selecting air sampling pumps to measure personal exposure.
IT IS estimated that every 30 seconds, somewhere in the world, one worker dies as a result of exposure to toxic chemicals, pesticides, radiation and other hazardous substances.1 The effects of exposure can develop quickly or take years to develop, leaving workers vulnerable to asthmatic and allergic reactions and longer-term illnesses such as cancer and cardiovascular, respiratory and nervous system disorders. While the cost to human health can be devastating, the financial costs to businesses through reduced productivity, employee absences, recruitment and compensation claims can be substantial.
Few workplaces are immune, as exposure can occur in businesses as diverse as healthcare, education, gardening, transport, office work and catering, whether from products used in the core of the company or for equipment maintenance and general cleaning.
Under the Workplace (Health Safety and Welfare) Regulations 1992, employers have a legal duty to ensure the health, safety, and welfare of employees as far as is reasonably practicable. This includes complying with the Control of Substances Hazardous to Health (COSHH). Under the COSHH Regulations 2002, employers must assess and implement measures to protect workers and those impacted by their workplace against exposures that could potentially be harmful to health.
A risk assessment must be conducted to gather information about which substances are present or likely to be present and who could be exposed and how. The health risks must then be evaluated to determine the chance of exposure occurring, how often the exposure is likely to occur, what level of exposure could happen, and for how long. Thus, monitoring for potentially dangerous airborne hazards plays a key part in overall risk management.
Industrial hygiene methods are geared towards measuring personal exposure using personal air sampling pumps because the tried-and-tested method can quantify personal exposure and ensure compliance with regulatory limits. A sampling pump’s size, weight, connectivity, and ability to access data are key, however, flow rate stability, pulsation, and back-pressure capability must also be considered. So, when purchasing a sampling pump, what features should you look for?
Many pumps are Intrinsically Safe (I.S.) rated as standard but it is worth checking that your pump’s I.S. rating is still appropriate for your facility to avoid any safety issues. An I.S. rated pump will not cause an explosion in a flammable atmosphere, critical for workplaces with significant levels of combustible substances. In addition, consider whether the pumps will be used in a harsh environment. For example, many pumps now have ‘Ingress Protection’ ratings, which means they are protected from ingress by water and dust.
Size, weight and accessibility are critical design elements. Pumps should allow freedom of movement, be unobtrusive, robust and not prone to leakage. Selecting a smaller, lightweight, low flow pump (0.05-1L) for sampling vapours and gases, over a medium flow pump (1-5L) equipped with a low flow adaptor is more user-friendly for workers.
When selecting a personal sampling pump, the battery life must be considered to maintain operation throughout the monitoring period. Lithium-Ion batteries are now starting to be used in the latest personal sampling pumps with significant advantages over traditional nickel-metal hydride and nickel-cadmium batteries. For example, li-Ion batteries have the highest energy density, which means that you need fewer cells and can ultimately achieve a smaller, lighter pump. Li-Ion batteries also do not suffer from the ‘memory effect’, meaning only part of the battery charge is usable. This will avoid having to change the batteries regularly or implement a battery management procedure.
It is vital to check that your pump meets the latest international standard for air sampling pumps. Compliance with ISO 13137 ensures accurate flow performance amongst other performance criteria, ensuring accurate sampling and meaning you will not have to repeat measurements.
The most significant factor to consider in the operational capabilities of your personal sampling pump is the choice of filter media. The smaller the diameter and pore size of your filter and the greater the flow rate, the greater the back-pressure exerted and the harder the motor needs to work. Membrane filters, as opposed to standard glass fibre filters, exert more back-pressure. If you use these filters routinely, check the back-pressure capabilities specified by your pump manufacturer. Will they cope?
Pulsation and air flow
The ISO 13137:2013 standard requires that the pulsation of a personal sampling pump shall not exceed 10 per cent of the flow rate. A pulsation measurement shows the difference in air flow between cycles; through every cycle, as the pump draws air in and expels it simultaneously, this exchange process causes an uneven flow. A large pulsation value means that if you are using a cyclone head for collecting respirable samples, flow does not remain steady, and the size cut of the respirable fraction is affected. To combat this effect, manufacturers include pulsation dampeners, which are rubber diaphragms that act as extra reservoirs of air to smooth the flow. Ensure that the pulsation values are within specification for your chosen pump.
Most pumps control the flow of air through the pump using a ‘constant flow’ mechanism. As back-pressure increases, the pump detects the change and alters the flow accordingly. At the end of the sample, flow should still be within plus or minus five per cent of the calibrated flow set at the start of the measurement. A constant flow ensures that you can be confident in the volume of air sampled for your exposure calculations.
Constant pressure control
‘Constant pressure control’ is primarily used for low-flow applications and allows the possibility of taking samples with sorbent tubes for gases and vapours. This method controls the flow rate by holding a constant pressure level in the tubing between the samplers and the pump. For many pumps, in order to do a low-flow measurement, you would purchase a separate constant-pressure controller. If you frequently undertake low-flow measurements, it is worth investing in a pump that has this built-in.
Connectivity and bluetooth
The latest generation of Bluetooth enabled pumps and flow calibrators can automate the calibration process and save valuable time, increasing confidence in the calibration results, which can be saved and/or emailed for reporting. Pulsation, once tested in a laboratory, can now be checked in the field at the same time as a normal flow rate calibration through an airflow calibrator equipped with Bluetooth. As advances in technology continue to develop, remote methods can avoid disturbing workers and improve the validity and reliability of sample data.
It is vital that these factors, alongside the broader environmental conditions in the specific working environment, are at front of mind when purchasing new equipment. Monitoring will help keep employees protected throughout the working day by ensuring air-sampling pumps identify hazardous amounts of fumes, dust and gases that increase the risk of long-term damage to worker health.
Tim Turney is global marketing manager at Casella. For more information, visit www.casellasolutions.com