Dhaka Metropolitan Police last week started using chloropicrin enriched pepper spray to control mobs.
Exposure to the new solution, stronger than tear gas, is injurious to human health, particularly eyes and the skin, experts said.
The police, however, claimed that the new gas spray was widely used to control mobs.
Dhaka University chemistry professor M Anwarul Islam said exposure to chloropicrin could cause severe irritation in eyes, lung and skin.
‘The gas spray we are using is internationally accepted and widely used to disperse mobs and it is completely non-lethal,’ DMP joint commissioner for public order management Shahhab Uddin Qureshi told New Age Sunday.
On Wednesday, DMP used the new spray for the first time to disperse school teachers demonstrating in the city to press their demand for monthly-pay order benefits from the government.
The use of the new spray left over 150 teachers injured including Esharat Ali, president of Non-MPO Shikkha Pratishthan Shikkhak-Karmachari Oikya Jote.
After receiving treatment at Dhaka Medical College Hospital, he said he still felt pain in his eyes and ears.
The new spray has reportedly been imported from China.
Around 50 teachers are still under treatment and some others left Dhaka for home with injuries in eyes and skin, he added.
The new spray was used on the agitating teachers on Thursday and Friday also to foil their scheduled demonstrations at Central Shaheed Minar leaving 100 more including some plainclothes policemen injured.
Sub-inspector Marmar Sing Tripura, who works in Ramna police deputy commissioner’s civil team, was affected when fellow policemen sprayed the new gas solution to disperse the teachers’ demonstration.
Visitors at DMCH told New Age that Marmar was seen shouting and screaming in pain.
Chloropicrin is an irritant having the characteristics of tear gas and intensely irritating odour.
Inhalation of one ppm of chloropicrin causes eye irritation, according to experts.
Bangabandhu Sheikh Mujib Medical University ophthalmology department chairman Sharfuddin Ahmed said primarily the patients should wash eyes with fresh water immediately after exposure to the spray. 
‘The patient needs steroid drop and antibiotic for the treatment. If anyone remains untreated, the victim in that case might lose vision,’ he said.
 The chemical can even damage lung and can cause death, he added.
Dhaka University pharmaceutical technology professor ABM Faroque said the same compound is used in tear gas also.
‘The use of chloropicrin enriched teargas is discouraged since it is injurious to human health, especially to eyes,’ he told New Age.
Faroque said it could even damage cornea and conjunctive in long run in case one is exposed to it repeatedly. 
The Food and Agriculture Organization in a document described ‘chloropicrin as a powerful tear gas. It is one of the most commonly used toxic fumigant for insects today. It is sometimes added in small proportions with other fumigants, specially, hydrogen cyanide and methyl bromide, to serve as a warning agent.
‘In humans, the immediate reaction of any person is to leave the vicinity in haste. If exposure is continued, it may cause serious lung injury,’ according to the FAO website.
Chloropicrin is used in agriculture as a soil fumigant also. It has also been used as a chemical warfare agent and a riot control agent. It was used in large quantities during World War I and was stockpiled during World War II.