5 Jan 2016
The UK offshore industry employs an estimated 33,664 people, according to 2014/15 statistics, who are exposed to a range of occupational health and respiratory risks including exposure to hazardous substances.
Monitoring of these hazardous substances uses
personal sampling pumps and the recognised manufacturing standard for pumps,
ISO13137, should ensure that all pumps operate to the same high level. With its
vast experience in scientific instrumentation, dating back to the 18th
century, Casella brings together its expertise in monitoring occupational dust
levels to explain that not all air sampling pumps are the same. Therefore if
you are in the market to purchase a new pump, here are the seven things you
should keep in mind to make the right decision.
A sampling pump’s
size and weight are key and also its connectivity and ability to access data,
much the same as a mobile phone, but in addition to that 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’s produced.
1. Battery life
Firstly, a
personal sampling pump’s battery life must be able to maintain operation
throughout a monitoring period. However, 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 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. Li-Ion
batteries have significant advantages over traditional NiMH and NiCd batteries;
they have the highest energy density meaning that you need fewer cells and this
means 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.
2. Wearability
Of course, the
wearability of a personal sampling pump is essential for making a monitoring
regime as non-disruptive as possible to 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, for
instance, to help in their engagement with the monitoring process. Also consider your need for decontamination,
how waterproof it is. Latest designs are
at IP65. Additional protection in harsh
environments is vital for the offshore oil and gas industry.
3. Ignition and
environment
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. At the centre
of the need for intrinsic safety is the part played by electronic design. The
definition of this from the standard IEC79-11 is:
“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. This protection of course has an impact on the potential
performance of the pump, for example, by limiting power to 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 harness potential losses. Look out for the I.S. markings on
your pump to ensure compliance.
4. Back Pressure
Capability
By far 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 during the course of the sampling, back pressure increases still.
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?
5. Pulsation and air
flow
The ISO13137:2013
standard requires that the pulsation of a personal sampling pump “shall not
exceed 10% 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, 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 a
filter. 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.
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 became blocked or shut off completely, the flow rate in the
other samplers remains constant. If this were a ‘Constant Flow’ 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 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.
All of these seven
factors are clearly a fine balancing act to achieve for product developers and
it is important that these factors, alongside the broad and diverse
environmental conditions in the oil and gas industry are at the forefront of the
health and safety professional’s understanding. Casella’s extensive experience allows
us to provide quality and highly suitable products to the industry, while also
offering the knowledge and expertise that once made us the choice of Charles
Darwin and now make us the choice of multiple industries worldwide.
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