How to signal industrial chimneys?

High-rise chimneys can pose an aviation hazard. To avoid aircraft collisions with these structures (obstacles) they should be signaled according to the suggestions of the International Civil Aviation Organization (ICAO), adopted by most countries in their national regulations.

Unless otherwise specified by the local aviation safety authority and apart from other possible forms of daytime signaling such as a structure painted in orange and white stripes, beacons and / or flags visible at long distances by the pilots of the Aircraft, in areas near aerodromes, chimneys must be marked with obstacle lights as follows as established by ICAO.

Chimneys up to 45m high:

Low Intensity lights installed at the highest possible height will be necessary, respecting a distance of 1.5 to 3m from the upper mouth of the chimney, to minimize contamination due to fumes guaranteeing light visibility.

Chimneys over 45m high:

Medium Intensity lights will be required, installed at the highest possible height, at a distance of between 1.5 and 3m from the upper mouth of the chimney. If the height is greater than 105m it will be necessary to install additional lights on intermediate levels.

The additional intermediate lights will alternately be Low Intensity Type B and medium intensity Type B or C lights (lately the trend is to install Medium Intensity Type C lights, fixed light, to avoid as much as possible inconvenience to the surrounding population) . The light levels will be evenly spaced between the upper lights and the ground level with a separation not exceeding 52m, and the necessary number of levels must be installed.

Chimneys over 150m high

If aeronautical studies indicate that the lights are essential for identification during the day, Type A High Intensity lights will be installed.
Depending on the height, intermediate levels should be installed, also for Type A lights. The spacing between light levels should not exceed 105m.

How many lights per level should be installed?

The signaling lights must be visible from 360º of Azimut around the obstacle. For this reason it is necessary to install the necessary number of lights so that the chimney can be seen from anywhere around it.
Specifically, the standard stipulates a minimum number of lights depending on the diameter of the chimney, according to the following specifications:

• Chimneys up to 6m in diameter: 3 lights per level
• Chimneys from 6 to 30m in diameter: 4 lights per level
• Chimneys from 30 to 60m in diameter: 6 lights per level
• Chimneys over 60m in diameter: 8 lights per level

In case of doubt or different interpretation of the regulations, the provisions of the local aviation safety authority must always be followed for each specific case.

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