Carbon dioxide - health hazard
Marine Notices 05/2003
The attention of Shipowners, Operators, Masters and crew is drawn to the dangers of exposure to high concentrations of carbon dioxide gas.
Though Carbon dioxide is a gas of low toxicity, it can cause asphyxiation and narcotic effects at high concentrations. Prolonged exposure to moderate concentrations can cause acidosis and adverse effects on calcium phosphorus metabolism resulting in increased calcium deposits in soft tissue. Carbon dioxide is a vasodilator, and is the most potent cerebrovascular dilator known. Carbon dioxide is toxic to the heart and causes diminished contractile force.
Carbon dioxide is an asphyxiant and toxic at high concentrations. At concentrations of three per cent by volume in air, it is mildly narcotic and causes increased blood pressure and pulse rate, and causes reduced hearing. At concentrations of about five per cent by volume it causes stimulation of the respiratory centre, dizziness, confusion and difficulty in breathing accompanied by headache and shortness of breath. At about eight per cent concentration it causes headache, sweating, dim vision, tremor and loss of consciousness after exposure for between five and ten minutes. Concentrations above ten per cent can be fatal. The gas does not give any warning of its presence in an asphyxiating concentration, and a person could become overcome before he/she becomes aware of the danger, and escapes.
The Exposure Standards Working Group recommends the following limits:
- TWA (Time Weighted Average) 5000ppm (9000 mg/m3 )
- STEL (Short Term Exposure Limit) 30000ppm ( 54000 mg/m3)
Personal gas monitors used in Australia have the low oxygen alarm preset to activate when the concentration of oxygen in ambient air falls to 19.5 per cent by volume. A three per cent concentration of CO2 in air will displace a proportionate quantity of the other gasses present, and the oxygen concentration will read as 20.27 per cent by volume on gas monitors. A five per cent concentration of CO2 in air will show an oxygen concentration of 19.88 per cent by volume in air. Both these readings are within the `safe' parameters for oxygen concentration requirements ie 19.5 per cent to 23.5 per cent by volume in air.
From the above it can be seen that safe levels of oxygen in air does not indicate safe levels of CO2 and mariners are urged to exercise caution in areas susceptible to CO2 contamination.
Areas on merchant vessels that could contain high concentrations of carbon dioxide include cargo spaces carrying raw timber and compartments containing fruits and vegetables, either as cargo, or for domestic consumption. All fresh produce is alive and must burn food reserves to keep alive. The chemical reaction that takes place is generally called respiration. Respiration involves the uptake of oxygen by the plant tissue to oxidise food reserves, usually sugars, to produce energy, carbon dioxide (CO2) and water. The energy produced is used to maintain essential life processes, while the CO2 and some of the water are `waste' products and are released to the surrounding environment. In a poorly or insufficiently ventilated compartment, this respiration will lower the oxygen level and increase the CO2 level. This process will actually increase the storage life of the produce by reducing its respiration rate.
Mariners are urged to exercise caution before entering compartments, which could contain asphyxiating concentrations of carbon dioxide. Spaces such as the CO2 room should be well ventilated prior to entry. For areas that cannot be adequately ventilated, the use of self-contained breathing apparatus or surface supplied respirator should be considered.
Clive Davidson
Chief Executive Officer
7 February 2003
Australian Maritime Safety Authority
GPO Box 2181
CANBERRA ACT 2601
File No: 030410
Term of Validity: Permanent
Internet address for all current Marine Notices: AMSA
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last updated: February 2003