At mineral processing sites, there are lots of substances that can remain airborne for days depending on the size of the particulate matter (PM).
There are sites that must mitigate against sulphur dioxide and other toxic gases with mild to dangerous health effects depending on concentration.
The emerging issue is diesel exhaust emissions emissions which are classified as DPM (Diesel Particulate Matter) these may be the some of the most hazardous exposures at underground mines and above ground operations. The composition of diesel particulate matter is complex and the reason that there is so much potential risk to health.
Diesel exhaust includes more than forty substances that are listed as hazardous air pollutants and fifteen are listed as carcinogenic to humans.
Furthermore, chemical reactions in the atmosphere contribute to secondary particulate matter reactions; again, with carcinogenic properties. Diesel combustion particles are made up of fine particles (PM 2.5) combined with a high level of ultrafine particles (PM 0.1) The particulate that is in the PM2.5 range deposit in the deep tissue of the lung exactly where the human body is not able to expel these.
The fraction at PM 0.1 has been shown to cross from airways into our bloodstream.
The solution is well ventilated areas with isolation measures and the best practice is to utilize a multitude of controls. An environmental cabin / enclosure equipped with fresh air pressurisations is the best practice to ensure a safe work environment for the operator (Doors and windows must remain closed always).
The cabin / enclosure must be installed with HEPA filtration to separate airborne fine particles.
The cabin / enclosure must also be equipped with an activated carbon filter phase to adsorb airborne ultrafine particles.
Sites in Western Australia utilising HEPA filters in a fresh air pressurised cabin have halved their exposure values.
BreatheSafe consulted with Meandu Coal Mine concerning airborne mine dust in their high voltage cabinets. A High Pressure HEPA Filtration system was specifically designed and installed on a Komatsu 830E HV cabinet with four TL pressurisers.
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).
