This note presents the results of a review of chlorine incidents reported to HSE over the period 1992-1998. It also provides details of the main sources of guidance on the storage, handling and use of chlorine. Chlorine and chlorine-based derivatives are reactive materials which are used in the chemical manufacture of a wide range of products such as paper, textiles, dyes, medicines, solvents, paints and plastics. Their oxidizing, bleaching and disinfectant properties are utilised in water treatment plants, swimming pools, food processing and in cleaning agents.
Incidents involving the release or unintentional production of chlorine gas
The information for the review was extracted from the MARCODE database (1992-1995) and from the FOCUS investigation database (1996-1998). All the incidents have been reported to HSE under RIDDOR (Reporting of Injuries, Diseases and Dangerous Occurrences Regulations) and have been investigated by HSE inspectors. 267 incidents were identified which involved the release or unintentional production of chlorine gas. These resulted in over 100 major injuries but there were no fatalities over the seven year period of the review. The incidents are very diverse and are categorised in terms of the activity involved:
- chemical processing;
- swimming pools;
- water treatment plants;
- food processing (includes dosing of products and disinfection);
- laboratories (schools) and ;
- cleaning agents.
The details are summarised in the table below.
Summary of chlorine incidents 1992 - 1998
Main causes of the incidents
Exposure to chlorine gas can occur in two ways: accidental release from a process or storage facility handling gaseous or liquid chlorine or the unintentional mixing of a chlorine derivative with an incompatible material. Only 51of the incidents involved the use of chlorine gas or liquid. This reflects the trend towards the use of chlorine derivatives for bleaching and disinfection systems. The use of chlorine gas or liquid is now largely limited to chemical manufacturing processes and major water treatment plants. Small scale bleaching and disinfection systems such as those in food processing plants and swimming pools are encouraged to use sodium hypochlorite or other chlorine derivatives. The causes of releases from systems handling chlorine gas or liquid were typical of process plant, in general. They included:
- corroded pipework;
- failure of seals and valves;
- mechanical damage;
- failure to isolate effectively;
- failure to follow procedures;
- operator error
The vast majority of the leaks were minor, some originating from routine operations such as cylinder or drum changing. They often resulted in injury or ill-health because operators and fitters failed to wear respiratory protective equipment. The main cause of incidents involving chlorine derivatives was the unintentional mixing of incompatible materials such as sodium hypochlorite and acid, releasing chlorine gas. Most water disinfectant systems involve dosing with sodium hypochlorite and hydrochloric acid in a controlled way. Although the hypochlorite and the acid may be segregated, they are still on the same premises, in the same building and often in the same room. There is scope for human error - primarily emptying chemicals into the wrong tank or container. The most common cause of incidents at swimming pools was topping up the hypochlorite tank with hydrochloric acid or vice versa. The causes of incidents at food processing plants is not so clear cut as there is a wider selection of processes and substances available. Most incidents were due to careless cross-contamination or failure to follow procedures eg discharging incompatible materials to drain. There were a number of offloading incidents where the driver offloaded into the wrong tank. These are potentially the most serious incidents as they can involve the mixing of large loaded into a tanker on top of an acid heel and there were two incidents during tanker cleaning.
The majority of the laboratory incidents occurred in schools during experiments to produce chlorine. Only small quantities of the gas were involved. Exposure to chlorine resulted because of faulty fume cupboards or while cleaning up after the experiment. Staff and pupils claimed to be affected. A large number of incidents involved the mixing of incompatible cleaning agents and water treatment chemicals. This indicates a lack of understanding of the hazards of these materials.
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