Containing deadly diesel emissions

If not properly monitored, diesel emissions can be deadly.

As part of the Occupational Health and Safety Act (OHSA), the Chamber of Mines published a Circular in 2012 with regard to Diesel Particulate Matter (DPM) exposure and its impact on employees. Yet there is still great concern that only a few companies are complying with regulations on diesel emissions reduction. One may ask: What is the root of the problem? Regulatory shortcomings and financial constraints Getting to the bottom of the matter, Andre Robberts, an expert in diesel emissions monitoring and control from John Ratcliffe, is not entirely surprised at the low level of compliance. He is of the view that the situation mirrors shortcomings with regulation protocols, as well as effective implementation of these regulations.

Also, Robberts says that low compliance may be due to the fact that mining companies have constrained financial resources, in an already embattled industry. “The big challenge that mines face is the financial implications on operating costs of implementing measures to comply.”

Implications of noncompliance

To some extent, the economic conditions might provide mitigating circumstances. However, failure to comply may have huge implications on their operations in both the short and long-term, Robberts cautions. “In the short term, poor compliance relating to the OSH Act can have an impact on operations and productivity due to high exposure limits. In the long-term, an organisation can experience an increase in legal costs. The high profile silicosis case claims illustrates the financial implications that could be borne should industry fail to act.”

International best practice

Fortunately, mining companies in Africa do not have to reinvent the wheel. In fact, the industry can save an enormous amount of financial resources if it adopts international best practices, Robberts suggests. He specifies the use of correct diesel emissions filters for effective diesel particulate matter emissions mitigation.

“Fit the correct system for each machine, as there is no ‘one-size-fits-all’ solution. Adherence to service intervals would allow for as little as possible human intervention. In the long run, fitting the right systems would result in a saving on both costs and maintenance, especially in the flameproof applications.” Robberts mentions the South32 mine project as one the classic examples of how mines can benefit from installing correct filters. John Ratcliffe was engaged as the project’s DPM emissions consultants. “Since 2013, after the diesel particulate matter filters were installed on selected machinery, there has been huge reduction in measured exposure limits.”

"Reference the Cancer aspect in the Chamber of Mines Circulation"
"Industry can effectively reduce diesel particulate matter emissions once regulations are tailored to create an enabling environment. This is the view of Andre Robberts, an expert in diesel emissions monitoring and control from John Ratcliffe."

No shortcuts

Nevertheless, Robberts cautions that shortcuts in diesel emissions reduction are bound to backfire. For instance, merely, replacing the diesel engines with Tier 4, 5 or even 6 engines will not help if there is no culture of maintaining these machines. That is why instituting training and maintenance is key. Also, it is worth mentioning that Africa does not have 5ppm diesel readily available locally. And so, it is critical that the emission systems that are implemented are able to handle the demands placed on machines in Africa. Industry can effectively reduce its emissions once regulations are tailored to create an enabling environment. For this reason, there is need for a clear direction from government on regulation guidelines and the timeframes of implementation. In this way, the private sector can be able to commit more financial resources towards emissions control.

Latest technology

New Sintered Metal Filter (SMF®) technology allows filters to be cleaned solely with compressed water eliminating the need for external ovens. The passive regeneration of theses filters can extend the service intervals up to 2000 operating hours. The ECU included in the system will monitor not only the DPF but can provide crucial information on the health of your machine. This allows for proactive  maintenance, rather than time lost due to preventable breakdowns. These systems are also compatible with 500ppm diesel and can be fitted on Tier2/Stage2 engines and upwards.

Diesel Particulate Filter on a Forklift

Forklift fitted with a HJS Diesel Particulate Filter

Carbon Monoxide and the Workplace

Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colorless, odorless, and tasteless, but highly toxic. It combines with haemoglobin to produce carboxyhaemoglobin, which usurps the space in haemoglobin that normally carries oxygen, but is ineffective for delivering oxygen to bodily tissues.

Concentrations as low as 667ppm, may cause up to 50% of the body’s haemoglobin to convert to carboxyhaemoglobin. A level of 50% carboxyhaemoglobin may result in seizure, coma, and fatality. In the United States, the OSHA limits long-term workplace exposure levels above 50 ppm.

The most common symptoms of carbon monoxide poisoning may resemble other types of poisonings and infections, including symptoms such as headaches, nausea, vomiting, dizziness, fatigue, and a feeling of weakness. Affected families often believe they are victims of food poisoning. Neurological signs include confusion, disorientation, visual disturbance, syncope and seizures.

"It should be noted that a purifier has a limited lifespan of between 5000 and 8000 hours."

This lifespan will be influenced by:

  • The performance of the engine
  • The quality of the diesel used
  • Airflow rate
  • Sulphur content of engine oil used

Whatever shapes the purifier take, the design principles are essentially the same. Each purifier consists substantially of a high-quality grade stainless steel case containing a ceramic honeycomb. The purifiers convert CO to CO₂ through a chemical reaction with the precious metal coating on the honeycomb monolith. This coating will with time be worn off, hence the need for a replacement unit.

What are the OSHA standards for CO exposure?

  • The OSHA PEL is 50 parts per million (ppm). OSHA standards prohibit worker exposure to more than 50 parts of the gas per million parts of air averaged during an 8-hour time period.
  • The 8-hour PEL for CO in maritime operations is also 50 ppm. Maritime workers, however, must be removed from exposure if the CO concentration in the atmosphere exceeds 100ppm.

Diesel Oxidation Catalysts (Purifiers/Catalytic Converters)

The John Ratcliffe diesel purifier starts to work at an exhaust temperature of around 120°C, thereafter its efficiency rises very quickly. At 230 °C, it removes over 80% of carbons; at 300°C, over 90% of carbon monoxide and over 80% of hydrocarbons, until at 350° C efficiency levels out, with the purifier eliminating over 90% of both pollutants.

As a forklift shifts heavier loads, it produces more pollution. With a purifier fitted, the greater the load, the more pollution is reduced. For example, at 1400 rev/min and full load, a typical diesel-powered fork-lift truck produces nearly 3000ppm of carbon monoxide; the purifier reduces this to around 270ppm – a reduction of over 90%.

The benefits of such purifiers are therefore:

  • High reduction of carbon monoxide to reduce dizziness and headaches, which affect the concentration of the operator.
  • Effective conversion of hydrocarbons and aldehydes. This translates to less eye and throat irritation. The diesel odours are virtually eliminated.

The Design

Purifiers are available in more than 400 different configurations to suit virtually every fork-lift truck and bus on the market. Whatever shapes the purifier takes, the design principles are essentially the same. Each purifier consists substantially of a high-quality grade stainless steel case containing a ceramic honeycomb.
This honeycomb supports a platinum-based catalyst that reacts with pollutants to form carbon dioxide and water as follows:

  • (Carbon Monoxide) 2CO + O₂ → 2CO₂ converted to harmless
  • (Aldehydes) HCHO + O₂ → CO 2 + H₂O converted to harmless
  • (Hydrocarbons) 4HC +SO₂ → 4CO₂ + 2 H₂O converted to harmless

High-technology research and development goes into each purifier model. For the optimum conversion of gases to occur, the maximum surface area of the catalyst has to come into contact with the maximum volume of exhaust gas. Yet the gas must not be blocked by the catalyst support in any significant way, otherwise engine efficiency will be impaired, hence the honeycomb design, which creates a turbulent gas-flow to force the maximum amount of gas into contact with the catalyst.

The cross-section of each cell in the honeycomb is made to particularly fine tolerances. The time path and optimum cell size (to allow the emissions to flow freely) and catalyst surface area (to allow the gas to react easily) are all crucial aspects of the purifier design. Each model is made to particularly heavy-duty specifications and is resistant to vibration. The purifiers are also compact, to fit into small engine compartments and should not interfere with normal engine maintenance.

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