Respirable mine dust in high concentrations cause lung disease due to overloading the defences of the respiratory system as particles start to deposit in the lung.
Silica airborne particles are 20 times more toxic to the lungs than coal dust alone; nevertheless, Silicosis is the world’s oldest known occupational disease. Workers who are exposed and inhale invisible Silica (RCS) particles are at increased risk of developing serious – and often deadly – silica related disease.
In the United States the Mines Safety and Health Administration (MSHA) has introduced a new rule that has lowered the concentration limit for respirable coal dust from 2.0 mg/m³ to 1.5 mg/m³.In regard to Silica the Occupational Safety and Health Administration (OSHA) new rule has been brought in and is expected that MSHA will follow suit. The new limit from OSHA’s new rule cuts the permissible exposure limit (PEL) in half from 100 to 50 micrograms (as an 8-hour time weighed average)
HEPA filtration system is effective at controlling respirable dust exposure as long as the operator remains inside.
The health risks associated with exposure to RCS can be controlled with the use of effective systems installed in environmental cabin/enclosures to isolate workers. Respirable crystalline silica (RCS) is one of major issues brought to the attention of the Queensland Parliament – Coal Workers’ Pneumoconiosis Select Committee Inquiry. The select committee will be looking at evidence of silica exposures of Brisbane’s tunnel workers.
“Silica is probably more dangerous than coalmine dust. We talked about the toxicities earlier. Quarriers, tunnelers, metal miners—anyone who is disturbing the earth’s crust and drilling through rock is at risk for quartz and silica exposure. There should be industrial hygiene monitoring of the exposure levels. We just lowered our exposure level to silica from 0.1 milligram per metre cubed to 50 micrograms or 0.05 milligrams per metre cubed because of the horrendous diseases that occur from silica.
Aside from the diseases we have already talked about for coalmine dust, silica is actually a lung carcinogen. It is an International Agency for Research on Cancer, IRAC, class 1 human carcinogen. It causes renal disease and causes other autoimmune diseases like rheumatoid arthritis and other things.”
Dr Cohen
To mitigate exposure to respirable dust a multitude of controls must be used. Then it should follow that fresh air pressurisation systems should be installed with HEPA filters in a two-stage setup: primary and return air stages to filter outside fresh air and also to filter the air that is inside the enclosure to same HEPA standard.
This process maintains the HVAC system dust free thus extending the lifecycle of the system and maintains the cooling capacity by avoiding air restrictions caused by dust contamination. These aspects must be considered, as it will result in costs reduction over the service life of the system. Specifically, reduce the overall costs of servicing & repairs of the HVAC system due to dust ingress contamination.
Finally, Its widely known and common practice that respirable fibres (Asbestos) must be removed using HEPA vacuum cleaners. The same principle applies in controlling respirable particulate inside the cabin.
The hidden risk factors from fine dust that impacts on the health and safety of operators.
The real issue is respirable dust (particulate) inside the breathing zone and the emphasis must be to prevent disease for the entire working life of operators. It is invisible to the human eye but it is found whenever extracted and processed minerals have been crushed, milled, screened, blasted, drilled, shovelled and conveyed.
Fine Dust Definition: “Dust of less than 10 microns which is capable of penetrating deep into the alveoli”
BSEN 481
The Task
Mining machines operate 24/7 in hot, dirty, dust-laden environments. Keeping the operator’s environment safe and healthy is an extreme task for equipment designers and maintenance crews.
In effect, the installed air quality (filtration) system is an essential component of a well-designed operator cabin. Environmentally controlled cabins reduce exponentially operator exposure to harmful particulates such as respirable crystalline silica, aerosols, particulate matter and other airborne contaminants or toxic gases.
The Risk
The very same respiratory hazards of fine airborne dust causes that shorten the life of air conditioning systems and other electrical equipment.
Dust exposure causes irritation and inflammation of the eyes and worsens pre-existing conditions. It has a drying effect with skin contact that can result in dermatitis. Prolonged exposure to fine dust results in increased nasal and respiratory conditions such as coughing. The result of high and prolonged exposure leads to inflammation of the lining tissue of the respiratory system with further complications such as bronchitis and pneumonia. Respirable dust (diameter <5 micron) is suspended in air that can travel to the deep tissue of the lung and pass through to blood stream associated with higher risks to health.
The Solution
The mitigation process is a multi-level approach with dust separation techniques with well-designed engineering controls.
There is evidence available to recommend BreatheSafe technology which can protect workers in situations where they are exposed to several respirable hazards from low to high exposure concentrations at their working environment in mineral processing sites, construction sites, waste and landfills and agricultural settings.
The methods to isolate and protect a worker are:
Integrated system The ecosystem BEGINS with a sealed (environmental) cabin with fresh air pressuriser in a climate controlled environment (HVAC). With the following features: HEPA filtration, auto pressure control, digital display with alerts and warning, remote monitoring, brushless long life pressuriser motor.
HEPA filtration The system to control respirable dust / particulate matter with a two-stage high efficiency filter media (Fresh air & return air filtration)
Remote monitoring / on board display Management of data to analyse and review internal environmental conditions and operator awareness/alerts that the system is working.
After conducting research and testing, BreatheSafe proposes a real-time dust monitoring study to evaluate the effectiveness of operator cabins working at mineral processing sites. This study focuses on bulldozers, front end loaders, and haul trucks. BreatheSafe evaluated that in order to keep cabin air safe with zero exposure, pressurisation of air was not enough.
Background
The belief that a machine cabin serves as a primary method for dust control needs to be reviewed. The risks associated with coal dust and silica dust exposure are now widely understood. Furthermore, there is scientific evidence which describes current worker exposure limits to low toxicity clouds of dust are not sufficiently protective.
An environmental cab must control the air inside. It must be pressurised to keep outside dust from entering through cracks in the window and door. The pressurised air must be filtered to keep out dust-laden air from entering the cabin. To limit the volume of air needed for pressurisation, doors and windows must be sealed.
However, there is no standard or guidance on the actual efficiency of the filters. In fact, there is no real protection for operators regarding hazardous substances below PM10. Established research demonstrates particulate matter below PM10 can reach the deep tissue in the lungs.
The latest calls from health organisations is for silica dust to be undetectable within the breathing zone of the operator. The same must apply for all other airborne hazardous substances that are present at mineral processing sites.
Essentially, a cabin by itself can no longer be assumed to resolve these problems and could be in some instances be more harmful to the operator. The goal for any solution is to provide a Zero Harm environment, and this requires more than cab pressurisation.
Types of controls
ISO 10263
The standard for machinery sold in Australia has been ISO 10263. This standard provides for 50 pascals of positive pressure when the cabin is new, with a minimum of 25 cfm airflow intake into the cab. To achieve this design standard, the cab is equipped with a filtered fresh air intake system and a filtered recirculating system and an air conditioner.
The cabin is sealed by rubber gaskets, tight latches and jambs which are placed on windows and doors. The typical volume of a cab is approximately two to three cubic meters and utilizes pleated cellulose media.
OEM paper filters do not provide any protection for respirable dust, allowing PM10 pollution to enter unhindered.
This standard is fundamentally applicable to provide airflow to aid the air conditioning system. Other issues arise when both intake and recirculation airflow are powered by the same fan, changing a filter(s) media without correcting the resistance on the system will lead to cabin pressure loss.
Furthermore, this type of environmental cab deteriorates quickly due to fine dust ingress. Therefore, will become ineffective requiring a retrofit for effective fine dust particle separation.
EN15695-3
This standard refers to the control of hazardous airborne substances for the protection of the operator in tractor sprayers (pesticides). This standard states an environmental cabin must be tightly sealed and provide greater than 99% efficiency for the fresh air filter.
Fundamentally, the minimum requirement of EN15695-3 is tested and certified filter media to EN1822 (HEPA H13) which guarantees air filtration down to 0.3 microns.
High-Efficiency Particulate Air (HEPA) filters are made from randomly arranged glass fibres thus airflow will be highly restrictive. These cannot be easily adapted for replacing OEM paper filters.
The INPRESS TL system that has been developed and tested for mine sites to succeed EN15695-3. It uses dual HEPA filters rated to minimum 99.97% efficiency with Auto Cabin Pressure Control (ACPC). It also includes a digital display that alerts the operator when there is a low-pressure event. The next issue is cabin sealing to effectively isolate the air conditioning system and to also isolate the operator.
This system has been designed for coal mines to provide a Safe Breathing Zone for the operator.
The cabin pressure setting can range from 20 to 100 pascals depending on the specific on-site requirements. Studies can be conducted to calculate dust load for a specific machine with remote monitoring.
Latest Guidance from Safe Work QLD (PN12377)
The following excerpt has been released form Worksafe Queensland for “Managing Respirable Dust Hazards in Coal-fired Power Stations for the Code of Practice 2018″
Isolation, segregation or enclosure of operations generating the dust
Relevant isolation controls include:
-Enclosed cabins with windows closed at all times
–Fitting high-efficiency air filtering systems (e.g. HEPA filters) to the intake and cabin recirculation air intake of front-end loaders, excavators and other machinery
-Keeping personnel vehicles dust sealed and pressurised.
We submit that a process of auditing of the cabin is included testing cabin sealing periodically and periodic testing with real-time dust monitoring instruments.
We also submit that machinery cabins be cleaned with a type H (HEPA) vacuum and never with brushes/brooms.
Methods of Evaluation
EVADE
The latest technical support by The National Institute for Occupational Safety and Health (NIOSH) is to audit a cabin and/or the operator with a real-time dust monitor and a portable camera. This indicates events for high peak exposures that have occurred consequently prevent future events.
Do you have dust in your cabin? Is the heating, ventilation and air conditioning (HVAC) system underperforming or not cooling as before? Has the machine been stood down often due to HVAC service or repairs?
If you answered yes to any of these questions, the main issue may be fine (respirable) dusts and the fact that for the most part these are invisible and can potentially remain airborne for days or weeks. Fugitive fine dust which become airborne is produced at mineral processing sites by blasting, shovelling, drilling, screening, crushing, conveying and handling.
Airborne Particulate Matter
Airborne particulate matter which has a diameter of less than 10 microns in size will pass through installed cabin filters easily that were never intended to mitigate against respirable dust in the first place. Settling dust may deposit inside the cabin surfaces, foot well and inside HVAC components (Evaporator). Hazardous conditions occur for the operator when internal deposited dusts are lifted by air conditioning-HVAC, machine vibration and operator body movements and consequently, internal dust contamination, become airborne inside the cabin without any means of capture. The installed cabin pressuriser- filtration system must be configured for respirable dust (Particulate) mitigation.
The best practice that applies and keeps an operator safe is the same practice and procedures that can be used to keep the HVAC system and the inside of the cabin clean. The same applies to reduce unexpected costs of unscheduled service cycles made up of components failures and/or HVAC system underperformance caused by fine dust contamination.
Reducing Service and Maintenance Costs
The following key points have proven effective in reducing service and maintenance costs:
Keep the cabin environment clean (Aaways keep doors and windows closed & use a HEPA vacuum in the cabin at least twice a week)
Pre-cleaner should be used to expel coarse particles and extend filter service life
Ensure fresh air pressurisation with a HEPA filter (High efficiency filter to control respirable particulate)
Use computer control pressurisation (Precisely control cabin environment and extend filter service life)
Employ computer cabin pressure controller with display and warning/alert for operator (Site management warning/alert by remote monitoring)
Have a brushless motor, with an operating design range between 10000 to 15000 hours of operation (Maintenance free)
Provide a HEPA return air filter to capture contamination from clothes and shoes (Keeps evaporator free from dust contamination)
Use remote monitoring for analytics 24/7 (May be used to develop filter maintenance intervals)
Maintain cabin integrity by replacing worn out seals (Audits as part of implemented dust management plan)
At site operations, a cabin is exposed to different concentration levels of dust. The operating environment may be subject to extreme levels of dust coupled with high ambient heat. When fine dust contamination begins to accumulate in the evaporator, the performance level decreases over time and eventually causes restrictions. This process of contamination increases heat load and it is the ultimate factor that causes HVAC failures.
US Legislation
The issue of occupational fine dust exposures has been studied and tested by NIOSH and OSHA in the US. Their findings are some of the key points discussed. There are further implications with silica exposure which is 20 times more toxic than airborne mine dusts and this has been a factor in the OSHA’s new ruling in the US which has significantly reduced the amount of silica dust exposure that a worker can be exposed to. The following is an excerpt form this legislation:
(iii) For measures implemented that include an enclosed cab or booth, ensure that the enclosed cab or booth:
(A)Is maintained as free as practicable from settled dust;
(B) Has door seals and closing mechanisms that work properly;
(C) Has gaskets and seals that are in good condition and working properly;
(D) Is under positive pressure maintained through continuous delivery of fresh air;
(E) Has intake air that is filtered through a filter that is 95% efficient in the 0.3-10.0 µm range
Breathe-Safe system: Digital display and controller, Precleaner, HEPA fresh air pressuriser, HEPA return air filter and equally
important – Cabin sealing.
Conclusion
The same system that keeps the operator safe will in fact reduce costs of unplanned maintenance and costs of HVAC repairs caused by internal dust contamination. The cost of a BreatheSafe (HEPA) fresh air pressuriser system is actually the same as a standard system. However, BreatheSafe has developed procedures and technology to help maintain costs by keeping a clean cabin and HVAC system. Furthermore, BreatheSafe has developed long life brushless motors to assist even further with keeping costs down of air filtration systems. Talk to us about reducing costs of entire system maintenance over the entire lifecycle of the machine whilst ensuring the most important aspect: keeping the operator breathing zone safe from respirable dust (particulate).
BreatheSafe aims to protect operators’ health when working inside a cabin or enclosure with the next key points being best practice, recommendations and topics to consider when selecting a protective system. A renewed health focus of mining operations is necessary and welcome. New imperatives will be recommended to protect the health of operators working in and exposed to respirable mine dust in above and below ground situations.
“The first priority and concern of all in the coal and other mining industry must be the health and safety of its most precious resource – the miner”
US Federal Coal Mine Health and Safety Act 1969 – amended 1977
Dangers of respirable dust in cabin
Respirable mine dust definition: airborne particulate which is <10 microns in diameter (PM10). These invisible particles can remain suspended in air for days or weeks with higher exposure levels when machinery is near areas of blasting, shovelling, screening, long wall mining and handling minerals.
These man-made particles can penetrate and deposit in air exchange part of the lung; the contributing cause is that our bodies lack of defence mechanisms to expel these particles. This allows particulates to remain in our lungs and continuously damage tissue. Even potentially entering our bloodstream. Larger particles (>10 microns) are filtered out in nasal passages, mucus membranes and conductive airways.
Silica is one the most common materials on the Earth’s surface but it is found as fugitive dust at mineral processing situations when mining materials have been crushed, milled, blasted and transported. This leads to the production or airborne respirable mine dust with particularly Silica dust that is around twenty times more toxic that coal dust.
Government recommendations and legislation
In the US, the Occupational Safety and Health Administration (OSHA) has directed a rule to lower Silica exposure level for US construction workers. The new standards protects workers from respirable crystalline silica exposures above the permissible exposure limit (PEL) of 50 μg/m3 , averaged over an 8-hour day.
The American National Institute of Occupational Safety and Health (NIOSH) has conducted several research projects with new and old equipment. The conclusions of these studies clearly show that high efficiency filters must be installed with fresh air pressurisation in adequately sealed cabins with high levels of confidence on the results; the evidence shows significant reduction of respirable mine dust contamination inside these cabins.
The following NIOSH table compares three markers of the effectiveness of cabin protection factors:
Best Practice Recommendations for Dust Regulation in Operator Cabins
These following are the main elements for protective systems in fixed and mobile plant equipment that is operating in hot, dust laden and harsh mine site environments:
Recommendation 1.
Cabin Sealing is required to limit external pollution from entering the cabin from wind penetration; door and window seals must be regularly inspected as part of a dust management plan and must be replaced along with fixing gaps and leaks inside the cabin. The higher the level of cabin sealing; will in fact make the system more efficient.
An earlier study by Cecala et al. [2002a,b] demonstrates the importance of Cabin Sealing and Pressurisation with a case study regarding respirable dust inside a drilling cab application:
Vehicle Cabin with new Air Conditioning System installed did not improve any dust controls inside Cabin.
Vehicle Cabin with new filtration with Pressurisation returned on average a protection factor of 52.
A cabin with a leakage model of 10% will require a higher volume of air to pressurise at 50 pascals than a cabin with a leakage model of 4% though ensuring fresh air volume exceeds a minimum of 30 m3/h to limit CO2 build up inside the enclosure.
The situation for a pressurised cabin with poor cabin sealing or broken seals is often a case where the HVAC system is struggling to cool down the cabin due to dust ingress and a higher volume of hot air due to leaks. Even though positive pressure may be achievable; it’s the hot air loading that is much higher than the ability of the HVAC system to control its climate. Ultimately delivering hot air to the face of operator whom will often open a door or window for additional ventilation rendering a protective system obsolete.
The other hazardous to health exposure that exists is when a cabin has become extremely contaminated with mine dust. Is the fact that the HVAC system will continue to recirculate respirable mine dust at the breathing zone of the operator inside the cabin.
Recomendation 2.
Fresh air pressurisation is the method to push against external particulate pollution from entering the cabin or enclosure which means that the operator must remain inside with doors and windows closed when the protection system is turned on. The studies conducted by NIOSH demonstrate that protection factors start at 10 pascals of positive internal air pressure. The European model for a one person sealed cabin is >20 pascal when there is a pressure gauge and >50 pascals for no pressure gauge operating a machine with hazardous airborne substances in agriculture.
The European best practice is: >20 pascals + HEPA media + Sealed cabin = High Protection Factor [EN156954-3 Cabin equipped with pressure gauge]
BreatheSafe Auto Pressure controls cabin pressurisation in real time in a dynamic process as pressurisation pre-set level is continually adjusted to cabin environment which is pre-set at >35 pascals.
Auto Pressurisation key points:
If a small loss of pressure is detected the system will automatically compensate.
If high level pressure loss is detected or pressure is below set point: low-pressure warning light will turn on to alert operator (option to add audible alarm is available plus further option for remote monitoring with remote alarm).
Event data will be recorded for future reference and/or record keeping.
System is only filtering volume of air required, on demand pressurisation.
BreatheSafe’s extensive onsite testing has demonstrated high system efficiency and extended filter service lifecycles when pre-set pressure is dialled in at >35 pascals positive pressure.
Recommendation 3.
HEPA filtration means installing fresh air pressurisation with HEPA filters to control respirable mine dust in the cabin. HEPA media is tested to European standard (EN1822) with 0.3-micron diameter particles to demonstrate an absolute level of performance at this particle size range defined as being the “Most Penetrating Particle Size” (0.3 micron MPPS). When testing for example: if 10000 particles (0.3 micron) are introduced to HEPA filter media a maximum of 3 particles can get through.
The best practice system delivers the highest protection factor when designed as two stage HEPA: fresh air (inlet) and HEPA (inside cabin) return air filter which captures contaminants introduced in the cabin from shoes or clothes.
Recommendation 4.
The pressure display is designed to inform operator that the protective system is working correctly and to alert operator when the system requires maintenance of if there is a fault that has been detected. BreatheSafe pressure display has data logging functions that can assist maintenance personnel to check for when filter media is approaching end of service life and replace filters accordingly. This data can also be used as chain of evidence that pre-set pressurisation [safe] level has been maintained over time inside the cabin.
Best practice protective system design is:
Cabin sealing: eliminate any contamination exposure from wind penetration.
Pre-Cleaner: separate up to 90% of coarse airborne debris & extend filer service life from premature dust loading
Pressuriser is to increase internal air pressure to push against airborne particulate.
HEPA filter (Fresh air) High Efficiency Particulate Arrestance filter media to separate respirable dust from entering the cabin.
HEPA return air filter: High Efficiency filter to clean air inside the cabin from shoes and clothes.
Digital display with warnings to inform operator that protective system is working and when it requires maintenance.
BreatheSafe system is readily available to be remotely monitored with automated data logging and alerts for mine site management.
Summary
The international best practice method is for cabins / enclosures to be pressurised above 20 pascals. Considering that positive pressurisation will only occur in a reasonably airtight cabin environment, sealing and sealing maintenance is esesential. The operator is required to keep doors and windows closed. Site operations to implement an effective mine dust maintenance plan to replace worn out cabin seals and to detect any air pressure leaks that can potentially be a source of cabin mine dust contamination.
In situations related to airborne respirable particles, to protect the operator, the requirements are to fit a fresh air cabin pressuriser system with HEPA filters rated at H13 or above. In situations with corrosive gases, an activated carbon filter is added to HEPA filters.
BreatheSafe has developed innovative technology to deliver safety for the health of operators working in harsh environments. High efficiency is required to reduce costs with proven outcomes providing the most reliable products for demanding 24/7 mine site operations. BreatheSafe ensures a cabin that delivers high protection factors along with high levels of comfort due to matching pressurising protective system to HVAC performance.
*Refer Euro Standard EN15695 for one person safety cabin fitted with high efficiency cabin pressurisation intended for mitigation of dusts and aerosols in agricultural sector. It is expected this standard will extend to construction equipment in future.
References
Cecala AB, Organiscak JA, Heitbrink WA, Zimmer JA, Fisher T, Gresh RE, et al. [2002a]. Reducing enclosed cab drill operators’ respirable dust exposure at surface coal operations with a retrofitted filtration and pressurization system. SME preprint 02-105. Littleton, CO: Society for Mining, Metallurgy, and Exploration, Inc.
Cecala AB, Organiscak JA, Page SJ, Thimons ED [2002b]. Reducing silica exposure in aggregate operations. AggMan Jan:24-28.
OHSA. (2018). OHSA Fact Sheet. OSHA’s Respirable Crystalline Silica Standard for General Industry and Maritime. Accessed 21/07/2021 from https://www.osha.gov/sites/default/files/publications/OSHA3682.pdf
