Lesson 13 – Metallurgical Plant Chemical Spills

CALCIUM CYANIDE: COP HAZARDOUS CHEMICALS

GENERAL:

Two types of emergencies are considered as most likely to occur, i.e.

• Spillage of cyanide from a storage vessel (contamination with some reactive substance may or may not follow).
• Contamination of cyanide with some reactive substance while inside a storage vessel.

SPILLAGE FROM A STORAGE VESSEL:

• Instruct someone to notify any senior official, and activate the emergency cyanide alarm.
• Put on full protective clothing including canister mask, and take immediate action to stop further spillage.
• Isolate the spillage (to minimise danger to humans and animals), and erect barricade around spill.
• Clear the affected area of personnel, and post guards on the up-wind side.
• Put warning notices up. “DANGEROUS CHEMICAL SPILL”
• Confine the spillage to the smallest area possible and make every effort to keep flakes dry.
• Cover the spillage with tarpaulins (to minimise effect of wind and rain).
• Divert any running water, which may come into contact with spill.
• Prevent or minimise entry of cyanide into storm water system.
• Clean up the spillage by loading it into suitable containers.
• Neutralize any material which cannot be cleaned with suitable neutralizing agent, e.g. ferrous sulphate, sodium or calcium hypochlorite’s.
• Should it be raining or spillage occurred on wet ground or standing water:

–Follow steps (1.a) – i) above.

–Evacuate personnel from occupied buildings nearby, especially on downwind side.

–Arrange for emergency team to be dispatched to the area promptly.

CONTAMINATION OF CYANIDE INSIDE A STORAGE VESSEL:

In the case of water contamination, which is the most probable, a certain amount of HCN gas will be generated, together with some acetylene.

• Evacuate all areas downwind of the cyanide vessel for at least 100 metres.
• Ensure that no smoking or naked flames is allowed within the same distance.
• In the event of an appreciable amount of water having entered the system, special measures will have to be applied to get the material out of the container.

The supervisor in charge should satisfy himself that the following equipment is available and in good order:

• Safety shower
• Fire extinguishers
• First aid equipment
• Emergency kits
• Air-line respirator
• Neutralising agent insufficient quantity

Discharge the material into suitable containers equipped with vented lids, with the accent being on skilled supervision and the issue of personal protective equipment.

Open the outlet of the system to the atmosphere.

Purge the system with dry air as soon as possible.

HYDROCHLORIC ACID (HCL):

GENERAL:

• Hydrochloric acid is a gas absorbed in water and increasing temperatures or decreasing pressures can result in the evolution of hydrogen chloride gas.
• Hydrochloric acid is extremely corrosive and fumes should be prevented from attacking metal work nearby.
• Heat generated by the reaction with other materials can cause a fire as hydrogen is generated.

SPILLAGE AND LEAKS:

There is a risk of spillage at all bulk handling processes, particularly when the material is under pressure or being pumped. In the event of a spillage occurring:

• Ensure that no persons have been affected.
• Notify the supervisor or senior official immediately.
• Put on full-length protective clothing and if concentrations are high or unknown, self- contained breathing apparatus must be worn.
• Take immediate action to rectify the cause of spillage.
• Remove all containers with chemicals etc. that can cause a reaction, from the area.
• Contain spillage to as small an area as possible and prevent acid from entering storm water systems.
• Recover as much spillage as possible and return to process or other storage.
• Evacuate all persons not in the emergency operation from the building or contaminated area.
• Dilute spilled acid with water to reduce fumes.
• Neutralize dilute solution with lime, soda ash or caustic soda.
• Test for effectiveness of neutralization.
• Flush away with excess water once neutralization process is completed.
• Check after flushing away that area is free of acid and alkali.

POINTS TO REMEMBER:

• Always recover spillage if possible.
• Small spillages can be flushed away with excess water.

SULPHURIC ACID (H2S04):

GENERAL:

• Concentrated sulphuric acid and its vapour rapidly destroy tissue and can cause very severe burns.
• Sulphuric acid reacts with metals to liberate sulphur dioxide or hydrogen, depending on the conditions of reactions.
• Hydrogen gas is highly flammable and forms an explosive mixture with air.
• Sulphuric acid in contact with organic matter can cause fire.

Reaction with water:

• The reaction of concentrated sulphuric acid with water is very violent and large quantities of heat are evolved. Care must thus be taken when diluting acid that no splashing due to localized boiling of the diluted acid occurs. Always add the acid to the water – never the water to the acid.

SPILLAGE AND LEAKS:

• Stock tanks and tanker off-loading site should be in a spillage area large enough to contain all likely spillage from tanks and tanker.
• The following protective equipment and clothing must be worn at all times:- Acid proof overall buttoned up to neck.
• Face shield.
• Goggles.
• Plastic gloves. Gumboots.
• Gasmasks (where necessary).

ACTION:

• Stop acid pump and close off delivery suction valves immediately.
• Stop leaks by plugging with rubber stopper or clamping, if at all possible.
• Evacuate all persons, not engaged in the emergency operation from the building or contaminated area to a position up wind from site.
• Before hosing is done, remember never to add water to the acid, first neutralize the acid with lime or soda ash.
• Dam large spills and leaks with ash, sand or dry earth for later recovery to process, or to effluent disposal site after neutralising with soda ash or lime.
• Disperse small leaks or spills with water spray or fog, use water cautiously to avoid spattering.
• Remove all combustible materials and such products as nitrates, carbides, chlorides and metallic powders from the area.
• Hose down with domestic water after acid has been neutralised