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Mercury can exist in several forms in nature and is a commonly-occurring compound, but the two forms of mercury often prevalent in refineries are elemental mercury and mercury sulphide.
Elemental mercury is the shiny silver liquid that most people think of when they hear the word ‘mercury’, the type found in old-fashioned thermometers. However, it is not the most common form of mercury, and is unstable in the presence of sulphur and some sulphur compounds. When exposed to these compounds, elemental mercury will form mercury sulphide.
Mercury is measured and controlled in offshore applications to prevent contamination risk to the environment as well as personal health. The Health & Safety Executive (HSE) lists the mercury workplace exposure limits (WELs) within their EH40 environmental hygiene guidance note.
Exposure to humans can happen via inhalation, contact with skin and eyes or ingestion. However, the predominant route of exposure to elemental mercury is by inhalation of vapours.
In its elemental form mercury exists as liquid metal, which in spite of its low vapor pressure (2 µm Hg), can be converted to a vapor at room temperature due to its low latent heat of evaporation (295 kJ/kg) and its relative absence from ambient air.
Due to the low vapour pressure of mercury compounds, airborne exposures are most likely during confined space entry or when contaminated equipment is heated. After inhalation, approximately 80% of mercury vapour crosses the alveolar membrane and is rapidly absorbed into the blood.
High, short-term exposure to mercury vapour may cause lung damage, nausea, vomiting, diarrhoea, increases in blood pressure or heart rate, skin rashes and eye irritation. Long-term exposure generally has a greater risk of harm to the human body, with frequent repeated exposures to low concentrations mostly targeting the nervous system and affecting the brain. This type of exposure may also affect the kidneys and developing fetus. Urine and blood testing are a common way of measuring employees’ exposure, as this tests for all types of mercury.
It is important to note that inhaled mercury has a half-life of approximately 1–2 months, which means 50% of the original quantity will still be present. Even low exposures over longer periods could result in the accumulation of mercury in the body at potentially toxic levels.
In many offshore and onshore applications, mercury monitoring is critical in measuring contamination risks from plant items that have the potential to release high levels of mercury when heated or irritated during maintenance and repair.
Recording the mercury concentration from any exposure during specific tasks like hot works, is important to both the environment and personal health.
If a worker is to carry out a task on a heavily contaminated piece of equipment the risk of exposure needs to be quantified beforehand. Simple yet effective steps, such as irritating the plant equipment to measure the mercury concentration prior to works as well as continued monitoring throughout the tasks, can be conducted.
It is known that mercury can have a significant impact on offshore plant equipment causing structural damage and increasing the risk of leaks and the levels of maintenance required to keep the plant operating safely and efficiently.
Real-time mercury monitoring solutions can offer powerful benefits. In the event of life-endangerment, real-time mercury concentrations allow surveyors to take preventive measures immediately. A blood or urine test can be conducted after a positive real-time concentration to ensure employee safety.
Other mercury measuring technologies utilise gold film technology. When the gold film becomes saturated with mercury, the instrument must be removed from the contaminated area for up to one hour to allow it to regenerate. This causes obvious delays to any project and increases the risk of exposure due to the instrumentation being removed from the working area.
The Mercury Vapour Indicator (MVI) from ION Science offers alternative technology for convenient and real-time mercury monitoring. The MVI does not require regeneration between readings, enabling constant monitoring throughout the unit’s battery life of more than five hours and eliminating downtime.
The MVI’s dual-beam UV technology uses photodiode detectors to measure the intensity of radiation passing through the sample chamber. The presence of mercury vapour will reduce the radiation energy reaching the photodiode detector in proportion to the vapour concentration. The optical system is designed specifically to detect mercury in the Ultra-Violet region of 254nm. This change is then converted into an electrical signal and conditioned to provide a linear reading on the LCD screen as µg/m3. MVI offers real-time monitoring of mercury down to 0.1 microgram per cubic meter in the workplace and is used in many applications across the world.
The unit offers two dynamic ranges of measurement (-0-200 µg/m3 with a resolution of 0.1 µg/m3 & –0-2000 µg/m3 with a resolution of 1 µg/m3) with the option to zero the unit in the field using a carbon filter. Each unit is pumped and draws the sample into the sample cell, sample probes of PTFE tubing can be attached simply to reach areas with a contamination risk.
With a response time of less than 3 seconds the MVI is an excellent solution for continuous real-time monitoring. The unit also offers an inbuilt audio alarm to alert workers when the concentration level has been exceeded, as well as a data logging feature.
The MVI is housed in a robust enclosure, offers simple operation and has a large LCD display. Unlike many other mercury monitors, the MVI is lightweight and with a sample probe is easy to use in one hand.
Shawcity offers exclusive UK-based servicing & calibration options for the MVI with a turnaround of just 10 days. We’re also manufacturer-approved, enabling full warranty protection.
The good news is the MVI is exclusively available to hire or purchase from Shawcity right now. To discuss your requirements or request a demonstration,
please contact the team on 01367 899553.