A guide to personal sampling pumps in the oil and gas sector
01 April 2016
The UK oil and gas industry employs an estimated 375,000 people, many of whom are exposed to a range of respiratory risks, including exposure to hazardous substances. Monitoring of these hazardous substances necessitates the use of personal sampling pumps and in this article, Casella Technical Product Manager Andrea Bowen gives a step by step guide on what to look for when sourcing these vital items of equipment.
A sampling pump’s size, weight, connectivity, ability to access data are key, much the same as a mobile phone, but in addition to this are considerations of flow rate stability, pulsation and back pressure capability. Also important is the environment that you’re working in: the temperature, the barometric pressure and the relative humidity, and also the filter media chosen. These factors impact upon the wearer, the occupational hygienist and most importantly upon the data set that is produced.
1. Battery life
Firstly, a personal sampling pump’s battery life must be sufficient to maintain operability throughout the monitoring period.
In both onshore and offshore environments the sampling pump can be put under widely variable levels of operating stress during a single monitoring period. As the filter media becomes loaded with sample, the pump has to draw harder to overcome backpressure, and this in turn draws more power from the battery.
As a result, Li-Ion batteries are now starting to be used in the latest personal sampling pumps. These have significant advantages over traditional NiMH and NiCd batteries - they have the highest energy density meaning that you need fewer cells and can ultimately achieve a smaller, more lightweight, 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 to the same extent as the other types. This means that you do not have to cycle the batteries regularly or implement a battery management procedure.
The wearability of a personal sampling pump is essential for making the monitoring regime as non-disruptive as possible for the worker. In the past, there have been instances where workers have removed the pump and put it in their locker until the end of the shift, so the latest generation of pumps include a motion sensor. This ensures that the pump has been worn and that the sample is therefore valid.
Choose a pump that can be worn comfortably by a variety of wearers - from large men to small women - to help in their engagement with the monitoring process. Different kinds of clothing should also be taken into account and other considerations include the need for decontamination and waterproofing – the latest designs are IP65 rated.
3. Ignition and environment
Explosion risk is always a possibility in the oil and gas industry which means it is vital that the pump must be intrinsically safe and not contain any ignition source. Look out for the I.S. markings on your pump to ensure compliance.
The relevant standard, IEC79-11, gives the following definition: “A circuit in which any spark or thermal effect produced in the condition specified in this International Standard, which include normal operation and specified fault conditions, is not capable of causing ignition in a given explosive gas atmosphere.”
Manufacturers must incorporate protective components into their circuitry at the very earliest stages of design. But this protection has an impact on the potential performance of the pump, for example by limiting power to the motor to ensure no spark and batteries are generally encapsulated, thus having an impact on size. The latest designs of pumps include mechanisms in the circuitry to counter any negative impact.
4. Back pressure capability
As regards the operational capabilities of your personal sampling pump, by far the biggest factor to consider 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, back pressure will also increase as the media becomes loaded during the course of sampling.
Membrane filters, as opposed to standard gravimetric GFA filters, exert more back pressure and so if using these filters routinely, check the back pressure capabilities specified by your pump manufacturer. Will it cope with your operational environment?
5. Pulsation and air flow
A pulsation measurement shows the difference in air flow between cycles. In every cycle as the pump draws air in and expels it simultaneously, the exchange process causes an uneven flow. The relevant standard, ISO13137:2013, requires that the pulsation of a personal sampling pump “shall not exceed 10% of the flow rate”.
A large pulsation value means that if you are using a cyclone head for collecting respirable samples, the flow becomes interrupted. The flow for cyclone heads must be exactly controlled because this affects the ‘size cut performance’, meaning less sample is collected and this obviously has an effect on your results. Even when collecting the inhalable fraction, pulsation has a serious effect with sample being deposited on the walls of the head instead of the filter.
To combat this effect, manufacturers include pulsation dampeners - 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.
In line with the standard and flow control, 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 this should be within ±5% of the flow set. A constant flow ensures that you can be confident in the volume data for your exposure calculations.
6. Constant Pressure Control
An additional method of control of flow is ‘Constant Pressure’ Control, which is primarily used for low flow applications and gives the possibility of taking multiple samples. This method controls the flow rate by holding a constant pressure level in the tubing between the samplers and the pump. This means that if one of the samplers becomes blocked or shuts off completely, the flow rate in the other samplers remains constant. In a ‘Constant Pressure’ control system, the pump would sense the drop in total flow from one of the samplers and the motor would speed up to compensate.
For many pumps, in order to do low flow measurement you would need to purchase a separate ‘Constant Pressure Controller’. If you do a lot of low flow measurements it is worth investing in a pump which has this built in.
7. Connectivity and Bluetooth
Whichever pump you choose, in the wider world, the use of smartphones and mobile devices are commonplace and it is unsurprising that this trend filters down into monitoring equipment. The use of Bluetooth low energy technology means that it can be included in pump designs without draining the battery.
This means that the occupational hygienist can remotely monitor, control and email data from the pump from 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 vital health and safety monitoring.
Conditions in the oil and gas industry vary widely, and different operators and contractors will have differing requirements for air sampling pumps. A careful assessment of the seven factors covered above should help users find the right type of pump to provide optimum protection to their workforce in the challenging circumstances found in onshore facilities as well as on the the oil and gas platforms off our coasts.
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