The Delhi government on Friday banned non-essential construction and demolition work as the air quality in the city worsened and brought the third level of the Graded Action Response Plan into force, reported The Times of India.

The Graded Response Action Plan has been devised by the Union government’s air quality panel which says that if the air quality is projected to reach the “severe” category, the restrictive actions under Stage III are to be invoked at least three days in advance.

On Friday, Delhi’s 24-hour average air quality index at 6 pm stood at 400 in the “severe category”, according to the Central Pollution Control Board data.

An air quality index between zero and 50 is considered “good”, 51 and 100 “satisfactory”, 101 and 200 “moderate”, 201 and 300 “poor”, 301 and 400 “very poor” and 401 and 500 “severe”. The AQI in the “severe” category “affect healthy people and seriously impact those with existing diseases”, according to the pollution control board.

The level 3 of the anti-pollution plan was imposed when the AQI was 399, according to The Times of India. The sub-committee on Graded Response Action Plan, at a review meeting, had said that the air quality was likely to slip into the “severe” category due to calm winds and stable atmospheric conditions.

With the ban, brick kilns, hot mix plants that are not operating on fuels and are not approved in Delhi and its adjoining areas, have to shut down operations, reported NDTV. Stone crushers, mining, and associated activities will be also banned.