Case Study: Comprehensive Mercury Vapour Survey in a Large Hospital Environment

Surveying buildings for the presence of hazardous materials prior to demolition is a critical safety measure that protects workers, the public, and the environment. The well-understood risks associated with asbestos have led to stringent regulations and compliance in the construction industry. However, a wide range of other hazardous materials pose significant risks, particularly in institutional buildings such as universities and hospitals. These buildings often utilise a variety of hazardous substances in their daily operations, including bulk chemicals, specialty chemicals and reagents, radioactive materials, mercury, lead paints, and polychlorinated biphenyls (PCBs). Identifying and managing these substances before demolition prevents accidental releases, ensures safe disposal, and mitigates the potential for harmful exposures. Comprehensive surveys are essential to uncover these hidden dangers and develop appropriate remediation strategies, safeguarding health and safety during demolition and subsequent construction activities.
 

 Mercury Contamination Project Focus and Survey Methodology

 
The focus of this project was to survey the building for hazards likely to be relevant in a hospital setting. The survey targeted the presence of radioactive nuclides, mercury, and specialty chemicals in specific parts of the hospital. This article concentrates on the mercury survey undertaken as part of this comprehensive evaluation.
 
Mercury is a potent neurotoxin, and its presence in the environment can pose significant health risks. It is used in various medical and scientific instruments and processes, making it a relevant concern in hospital settings. The mercury survey employed multiple methods to ensure a thorough assessment of potential contamination and exposure risks.

 Mercury Risk Monitoring Methods

 

 Mercury Pumped Sampling

 
Pumped sampling involves actively drawing air through a sampling device over a specific period, typically 8 or 24 hours. This method is particularly useful for evaluating personal exposure of operatives in compliance with the Control of Substances Hazardous to Health (COSHH) regulations. The samples collected can be analysed to determine the concentration of mercury vapour in the breathing zone of workers, providing critical data on occupational exposure levels. This method helps in understanding the immediate risk to individuals and ensuring that exposures do not exceed the Workplace Exposure Limits (WEL).
 

 Mercury Passive Sampling

 
Passive sampling methods involve placing samplers in the environment for extended periods, usually one to two weeks. These samplers do not require a power source or active air movement, making them suitable for long-term monitoring. Passive sampling provides an average concentration of mercury vapour over the sampling period, offering insights into the ambient levels of contamination. This method is particularly useful for identifying areas with chronic low-level exposure and assessing the effectiveness of ongoing control measures.
 

 Mercury Vapour Direct Reading Instruments

 
Direct reading instruments, such as portable mercury vapour analysers, provide immediate feedback on mercury concentrations in the environment. These instruments are best suited for contamination tracking and source identification surveys. They allow for real-time measurements, enabling quick identification of mercury hotspots and potential sources of emission. This method is invaluable for conducting detailed surveys of specific areas, such as laboratories, storerooms, and maintenance areas, where mercury-containing equipment and chemicals are used or stored.

Mercury Contamination Sources in the Hospital Environment

 
In the hospital setting, mercury would most likely have been used in several key areas, particularly in medical and diagnostic equipment, laboratories, and maintenance departments. Common procedures and tools involving mercury include thermometers, sphygmomanometers (blood pressure monitors), dental amalgams, and certain laboratory reagents. Mercury could have escaped into the environment through breakages, spills, improper disposal, and during equipment maintenance or replacement. Over time, mercury vapour can accumulate in poorly ventilated areas, such as storerooms, basements, and maintenance workshops. Additionally, mercury may seep into cracks and crevices in flooring or be absorbed by porous materials like wood and carpet, leading to prolonged contamination and the need for thorough monitoring and remediation efforts.
 
Accidental small spillages of mercury can accumulate in areas where mercury-containing tools and equipment were frequently used, such as patient examination rooms, laboratories, and maintenance workshops. When devices like thermometers or sphygmomanometers are broken or improperly handled, tiny droplets of mercury can be released. These droplets can scatter and become lodged in cracks, crevices, or porous materials, making them difficult to clean up completely. Over time, even small amounts of mercury can accumulate and lead to persistent, long-term contamination in these frequently used areas.

Persistence of Mercury Vapours in the Indoor Environment

 
Under ambient conditions, mercury can evaporate slowly, releasing mercury vapour into the air. The evaporation rate of mercury increases with temperature, meaning that warmer environments can exacerbate the release of mercury vapour. At room temperature, mercury has a vapour pressure of approximately 0.0012 Pa, which allows it to gradually evaporate and contaminate the air over time. This slow, continuous release of mercury vapour can result in chronic exposure for individuals who spend significant amounts of time in contaminated areas.
 
The complete evaporation of mercury from a typical medical thermometer, which contains about 0.5 to 1 gram of mercury, under ambient conditions at 20°C would take a significant amount of time. This is due to mercury's low vapour pressure and slow evaporation rate of approximately 0.01 mg/cm²/hour at room temperature. Assuming an exposed surface area of around 1 cm², it would take roughly 50,000 hours (approximately 5.7 years) for 0.5 grams of mercury to evaporate, and about 100,000 hours (approximately 11.4 years) for 1 gram to fully evaporate. These considerations underscore the persistent nature of mercury contamination and the critical need for prompt and thorough clean-up of any mercury spills to prevent long-term exposure and health risks.
 
To estimate the ambient concentration of mercury in a room with a volume of 10 cubic metres, we consider the evaporation rate and the amount of mercury. Assuming a medical thermometer contains 0.5 to 1 gram of mercury and given the evaporation rate of 0.01 mg/cm² per hour at room temperature, we can calculate the concentration increase. For simplicity, assuming the mercury droplet has a surface area of 1 cm², 0.01 mg of mercury would evaporate each hour. In a room of 10,000 litres (equivalent to 10 cubic metres), this results in a concentration of approximately 0.001 mg/m³ after one hour. This concentration would gradually increase over time if there is no air exchange, leading to higher levels of mercury vapour in the air.
 
Long-term, low-level exposure to mercury vapour can have serious health effects. Chronic exposure to mercury can affect the nervous system, leading to symptoms such as tremors, mood swings, irritability, insomnia, headaches, and cognitive impairments. In severe cases, it can cause more pronounced neurological symptoms, including muscle weakness and impaired coordination. Additionally, mercury exposure can impact the kidneys, causing proteinuria and nephrotic syndrome, and can also harm the respiratory system. Given these risks, it is crucial to identify and remediate areas of mercury contamination in hospitals to protect the health and well-being of staff, patients, and visitors.

Hospital Mercury Survey

 
To survey the large hospital structure, we employed direct reading instruments, focusing on areas where mercury was likely to have been used and could have accumulated over time. These instruments allowed for real-time measurements, providing immediate feedback on mercury vapour concentrations. We systematically examined patient examination rooms, laboratories, maintenance workshops, and storerooms over several days. This thorough approach ensured that we covered all potential hotspots of mercury contamination. The detailed information gathered from the survey enabled the client responsible for the safe demolition of the building to make informed decisions. Our findings indicated that no areas had significantly elevated mercury levels, allowing the client to proceed with the demolition project according to the agreed timelines without incurring additional decontamination costs. By providing accurate and timely data, our service added significant value, ensuring the client's project remained on schedule and within budget, and reinforcing our commitment to safety and efficiency.