safety

Some reagents used in water treatment are hazardous products (acids, bases, chlorine, ammonia, ozone among others).

Large storage units for acids, sodium hydroxide or chlorine are governed by extremely stringent official regulations which must be referred to in each country.

Stipulations concerning chlorine leaks are especially important when storage requires a neutralisation unit to cover for the eventuality of a chlorine leak; the chlorinated air to be neutralised is drawn up by a blower and then delivered into the bottom of a column where a neutralising solution backflows (lye only or lye combined with sodium hyposulphite) through contact rings.

In view of the serious dangers that can arise should chlorine leak, it is compulsory for storage premises to be equipped with efficient leak detectors.

The flow rate of a chlorine gas leak from a storage container can only be sustained in the presence of an outside source of heat, through the container’s walls, equivalent to the liquid chlorine vaporisation heat at the flow rate concerned. Furthermore, when the pressurised gas is expanded and flows through the leak opening, there will be a drop in temperature that will tend to reduce the leak flow rate. For these reasons, we need to avoid spraying or submerging the storage tank in water, except in the case of small chlorine cylinders where there are no chlorine leakage neutralisation systems and where the only solutions, should the cylinder valve become jammed, consist of submerging the cylinder into a neutralising solution.

Apart from existing regulations, elementary common sense precautions must be taken (even when they are not legally compulsory) when handling and storing these products. The following recommendations apply:

• wearing a hood, goggles, gloves and a safety apron whenever working on a circuit carrying a corrosive product;
• installing specific safety showers and eye-baths in the vicinity of acid and sodium hydroxide storage and transfer areas;
• constructing retention pans (not connected to the mains sewer) beneath acid and sodium hydroxide tanks, with separate pans when acid and sodium hydroxide are stored in the same place;
• clearly labelled transfer pipes in order to minimise potential dangerous combinations when certain reagents are delivered (e.g. acid/hypochlorite);
• systematic maintenance carried out on pipelines and gas scrubbing devices fitted on hydrochloric acid tank vents since hydrochloric acid vapors will irritate the mucous membranes in the respiratory tract (and since these vapors are also corrosive for neighbouring equipment);
• draining of all low points on hazardous reagent circuits so that maintenance tasks can be undertaken in complete safety;
• when diluting crystallised or anhydrous ferric chloride, quick lime, sulphuric acid and sodium hydroxide, beware of heating that can be violent (see chemistry and reagents figures 19-21-26);
• powdered activated carbon, as a dust suspended in air, is subject to spontaneous ignition. Work and flames are prohibited in the premises concerned. These premises are normally equipped with a ventilation and air filtration system.