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.
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
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.
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
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.