What happened?
The Motorman noticed that the level in the sodium hypochlorite (NaOCl) dosing tank at the sewage treatment plant (STP) was low. He intended to refill the tank but, inadvertently and without realizing it, had taken a different chemical – namely, a 38- to 40-percent sodium bisulphite (NaHSO₃) solution – from the chemical store. When the NaOCl solution still in the dosing tank mixed with the NaHSO₃ solution that had been added, an exothermic chemical reaction occurred, releasing toxic gases and causing the plastic dosing tank to burst. The personal protective equipment (PPE) selected did not protect the Motorman’s body from
contact with the chemical mixture, resulting in minor injuries from chemical burns and the violent impact of the bursting container. The Motorman received first aid. Since the ship had cast off in the meantime, he was taken ashore by pilot boat and subsequently transported to the hospital by ambulance.
Why did it happen?
The accident was caused by an accidental mix-up (slip) that went unnoticed until NaOCl and NaHSO₃ mixed in the dosing tank and reacted violently. The plastic NaOCl dosing tank ruptured as a result of the exothermic reaction
− The dosing tanks were difficult to access, which is why they had to be moved to another location for refilling;
− The cramped installation of the chemical containers on the STP made it difficult both to replace them safely and to see the safety signage, which was mounted low;
− Due to the design of the STP and the shape and size of its storage containers, highly reactive chemicals had to be transferred manually, thereby increasing the risk of contact;
− The Motorman had not familiarized himself with the Material Safety Data Sheets (MSDS) for the STP chemicals; his supervisor had not informed him of the properties or hazards of the chemicals; and the Motorman had not received any operational training on handling chemicals;
− The multi-page MSDSs did not contain clearly stated relevant safety instructions, which meant that the hazards associated with combining the two chemicals were not known and could not be readily identified;
− In the manufacturer’s manuals and on the STP dosing tanks there was very little information or warning labels;
− The distinction between the black and white plastic trays beneath the dosing tanks was not immediately apparent. Both dosing tanks/containers were the same color (white) and were not color-coded accordingly; − Because a transfer container was used, the labeling on the chemical storage container and its color could not be compared with the signs on the dosing tank holder or the color of the plastic trays;
− The PPE worn when the dosing tank ruptured did not provide adequate body protection against the released chemical mixture.
What can we learn?
− Avoid manual decanting: Where possible during the plant design stage, hazardous chemicals should be supplied in such a way as to eliminate the need for decanting, e. g. by directly replacing the chemical containers. Where this is not possible, technical
measures should be taken to minimise contact with the substances.
− Allow sufficient space: When planning engine rooms, manufacturers’ specifications and operational requirements must be taken into account to ensure that maintenance and container changes can be carried out safely.
− Check safety barriers: Signage, labelling and colour-coding must be checked regularly – particularly when operating conditions change – to ensure they remain effective. They must be clearly visible and must not be obscured or interrupted.
− Clearly label chemicals: Where several hazardous substances are used at a single plant, containers, tanks, holders, trays and, where applicable, transfer containers should be clearly and consistently labelled and colour-coded, respectively. Appropriate measures must be taken to prevent accidental mixing.
− Warn of hazardous mixtures: Where substances may react dangerously on contact, explicit warning must be given of the consequences of mixing them. These consequences may be considerably greater than the hazards posed by the individual substances and may therefore require more stringent protective measures.
− Make safety information user-friendly: MSDSs, safety management documents and other instructions should be clear, concise and unambiguous so that they are actually consulted before work begins and any existing risks or hazards are identified.
− Design decanting systems safely: Decanting containers and funnels should be incorporated into the existing colour-coding system. Designated containers and funnels can also reduce the risk of reactions caused by chemical residues when reused.
− Assess unplanned work too: A risk assessment should be carried out before undertaking unplanned work. When handling chemicals, MSDSs or other substance-specific information, as well as PPE requirements, must be observed. -Combine eye protection: Even when using face protection, close-fitting chemicalresistant goggles or safety goggles with side protection should be worn. A visor that is open at the sides does not, on its own, provide equivalent eye protection; however, it may be appropriate as part of full-face protection.
− Assess incidents before casting off: If an accident or incident occurs shortly before departure, the first step should be to ascertain the nature of any injuries and damage and whether casting off needs to be postponed. As a rule, only minor injuries can be treated
safely on board; technical damage may pose additional risks during manoeuvring inside the port.
In the event of occupational accidents involving chemicals, the MSDSs for all substances involved should be provided to the emergency services upon handover. These can be crucial for treatment, particularly if the person affected is unable to describe the circumstances of the accident or the substances involved themselves.