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Workers in the offshore oil and gas industry are exposed to a range of hazardous substances that could impact their occupational health, increasing the likelihood of developing respiratory conditions, among others. Personal sampling pumps are a tool used to monitor such substances. A sampling pump’s size, weight, connectivity, and ability to access data are key, but in addition to that are considerations of flow rate stability, pulsation, and back-pressure capability.
When purchasing a sampling pump, what features should you look for?
A personal sampling pump’s battery life must be able to maintain operation throughout a monitoring period. Due to the variable nature of the offshore oil and gas environment, the sampling pump can be put under changeable amounts of operating stress during a single monitoring period. As the filter media becomes loaded with sample, the pump must draw harder to overcome back pressure, and this in turn draws more power from the battery.
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. 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” (where only part of the battery charge is usable) or lose charge through storage, meaning you don’t have to cycle the batteries regularly or implement a battery management procedure.
The wearability of a personal sampling pump is essential for making a monitoring regime as non-disruptive as possible to the worker. The latest generation of pumps now includes a motion sensor ensuring the pump has been worn and the sample is valid. Choose a pump that can be worn comfortably by a variety of wearers to help in their engagement with the monitoring process.
The possibility for explosive situations in the oil and gas industry means it is vital that the pump must be intrinsically safe and not be a source of ignition. The latest pump designs include mechanisms in the circuitry to harness potential losses. Look out for the I.S. markings on your pump to ensure compliance.
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.
The biggest factor to consider in the operational capabilities of your personal sampling pump is the choice of filter media. The smaller the diameter and the 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. Furthermore, as the media becomes loaded, back pressure increases still.
Membrane filters, as opposed to standard gravimetric GFA filters, exert more back pressure. If you use these filters routinely, check the back-pressure capabilities specified by your pump manufacturer. Will they cope?
The ISO 13137:2013 standard requires that the pulsation of a personal sampling pump “shall not exceed 10 percent 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 by means of a “constant flow” mechanism. As back pressure increases, the pump detects the change and alters the flow accordingly. According to ISO13137, should be within plus or minus 5 percent of the flow set. A constant flow ensures that you can be confident in the volume data for your exposure calculations.
“Constant pressure control” is primarily used for low-flow applications and allows the possibility of taking samples with sorbent tubes for gases and vapors. 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 low-flow measurement, you would purchase a separate constant-pressure controller. If you do a lot of low-flow measurements, it is worth investing in a pump that has this built in.
The use of smartphones and mobile devices is commonplace, and it’s unsurprising that this trend filters down into monitoring equipment. Bluetooth low-energy technology can be included in pump designs without draining the battery. This means that industrial hygienists can remotely monitor, control, and email data from the pump to their mobile phone without having to disturb the worker. The unique locations of offshore oil and gas sites make this remote technology an ideal investment for health and safety monitoring.
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. As the oil and gas industry looks set to get busier than ever, ensure that you’re able to monitor worker exposure as effectively as possible.
Tim Turney, Technical Product Manager Casella
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This article was first published in the AIHA online magazine