Carbon Monoxide and the Workplace
Carbon monoxide poisoning is the most common type of fatal air poisoning in many countries. Carbon monoxide is colourless, odourless, 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.
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 affects 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. 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 takes, the design principles are essentially the same. Each purifier consists substantially of a high-quality grade stainless steel case containing a ceramic honeycomb.
The purifier converts 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.
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 go 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.
