Ammonia is one of the most common industrial chemicals. It has been used as an industrial refrigerant for more than 120 years and is still the most popular industrial refrigerant in the world, though not in Hong Kong.

Ammonia solution in water is available to the public in chemical shops along with other industrial chemicals such as sulphuric acid, hydrochloric acid and caustic soda.

Most of these industrial chemicals are classified as 'toxic' under the Dangerous Goods Ordinance.

In fact, the ammonia solution that was used by the cleaner is much less toxic than any one of the three industrial chemicals named above.

It is less toxic than hydrochloric acid, although both chemicals, at dilute concentration, can cause extreme irritation and are commonly used as cleaning agents.

Another common cleaning agent is the liquid bleaching solution we use in laundry, which is the most toxic of all common cleaning agents when mixed with an acid and undiluted.

The irony is that the worker who scrubbed the staircase with the ammonia solution was unharmed. He worked from the top floor down without wearing a mask.

As an industrial chemist, I know that the firemen would have found it hard to breathe in their chemical protection suits and masks if they hadn't used them correctly.

I'm also sure the doctors at Queen Mary Hospital found all five of the firemen and the family recovering satisfactorily.

This is because the amount of ammonia used by the cleaner could not have released a high enough concentration of the chemical to cause sustained injury.

Ammonia in the air can be detoxified quickly with carbon dioxide.

It reacts with carbon dioxide and water to form ammonium bicarbonate which is totally harmless to plants and animals. The amount of ammonia used by the cleaner should not require more carbon dioxide for detoxification than the content of one small fire extinguisher. One experienced firemen could have done the job.

K. N. WAI Taikoo Shing