Smoke control: stair pressurization and smoke extraction

In short

According to NIST, about 70–75% of fire victims in the US die from smoke inhalation, not from burns. Smoke control keeps smoke out of the escape routes in two ways. Pressurization blows outdoor air into stairwells, lift shafts and airlocks, so they stay at a higher pressure than the floor on fire. Extraction pulls smoke out of corridors, halls and atria. Ordinary ventilation has to stop at the same time, or it spreads the smoke through the building. The minimum pressure difference is 12.5 Pa in a sprinklered building under the US standard NFPA 92, and 20 Pa under the Russian and Azerbaijani norms. The upper limit keeps the doors light enough for people to open.

Smoke kills more people than flames

• In US residential fires in 2017–2019, smoke inhalation alone was the main cause in 35% of civilian deaths, burns and smoke together in 49%, and burns alone in 6%. These shares cover the deaths where a cause was recorded (US Fire Administration).
• NIST, citing an NFPA report, puts the share of US fire victims who succumb to smoke inhalation at about 70–75%.
• John Klote of NIST notes that stairwells and lift shafts often fill with smoke, which blocks evacuation and gets in the way of firefighters.

How smoke travels through a building

• The forces. Klote lists the stack effect, the buoyancy and expansion of hot gases, wind, the fans of the ventilation system and the piston effect of moving lifts.
• Stack effect. When it is cold outside, air rises through stairwells and shafts. In air-conditioned buildings in hot weather, the flow can reverse and run downward.
• The ventilation system itself. Klote advises designing it so that, when fire is detected, its fans either stop or switch to a smoke control mode. Otherwise, he writes, "the HVAC system will transport smoke to every area the system serves."

Keep the smoke out, or take it out

NFPA 92, the US standard for smoke control systems, covers both approaches. Containment uses pressurization of stairwells, zones, lift shafts, vestibules and refuge areas. Management deals with large spaces such as atria, removing smoke with fans or natural vents. Both start automatically from fire detection: a sprinkler flow switch, a smoke detector or a heat detector. NFPA 92 says how to design these systems; whether a building needs one is decided by the building and fire codes.

Russian law uses the same two tools. The fire safety regulation (Federal Law 123-FZ) lists supply air that creates overpressure in protected rooms, airlocks and stairwells, and mechanical or natural smoke exhaust. Since July 25, 2022, pressurization without smoke exhaust has not been allowed. Under the Russian code SP 7.13130, smoke exhaust is required, for example:

• from corridors and halls of residential, public, administrative and multi-use buildings taller than 28 m;
• from corridors longer than 15 m without natural ventilation, in public, administrative, multi-use and some industrial buildings of two or more storeys;
• from corridors connected to smokeproof stairs;
• from atria and passages.

Azerbaijan's HVAC design code AzDTN 2.12-2* requires smoke exhaust from corridors of industrial, public and administrative-amenity buildings taller than 26.5 m.

For blocks of flats in England, the guidance in Approved Document B describes natural smoke vents: a corridor vent of at least 1.5 m² on an external wall, or a smoke shaft of at least 1.5 m², plus a vent of at least 1 m² at the top of the stair.

Stair pressurization in numbers

* As reported by CIBSE Journal; we did not see Table 1 of EN 12101-13 itself.

The 2022 European standard EN 12101-13 replaced EN 12101-6:2005 for the design of these systems. It covers buildings up to 60 m, defines two classes (Class 1 and Class 2), drops the old 10 Pa scenario and keeps the protected space at positive pressure at all times.

Why normal ventilation stops in a fire

• Russia. When smoke ventilation starts, general and process ventilation and air conditioning must shut down, except systems that keep a process safe (123-FZ, Article 85). SP 7.13130 adds that normally open fire dampers close on the fire alarm signal. The smoke exhaust fans start 20–30 seconds before the supply fans.
• Azerbaijan. In buildings with automatic suppression or a fire alarm, AzDTN 2.12-2* requires an interlock that stops the other ventilation, starts the smoke ventilation, opens the smoke dampers and closes the fire dampers on the floor or zone on fire.
• USA. Under NFPA 90A, duct smoke detectors are installed in supply systems above 944 L/s (2,000 cfm), and in return systems above 7,080 L/s that serve more than one storey. They stop their fans on detecting smoke. Codes based on the International Mechanical Code put detectors in the return air of systems above 2,000 cfm instead; the detector shuts the system down, or switches it to smoke control mode if it is part of one.
• Not with gas suppression. Russian law forbids running gas, powder or aerosol suppression and smoke ventilation in the burning room at the same time; see our article on gas suppression systems.

The shutdown is not absolute. NFPA 92 allows "nondedicated" systems that reuse HVAC fans in a changed mode, and Russian law keeps process safety systems running.

Fire dampers and smoke dampers

• Fire damper. It closes automatically when heat is detected and stops fire passing through ducts in fire-rated walls and floors. In Europe it is covered by EN 15650. A "static" fire damper may only be used where the ventilation system shuts down automatically in a fire.
• Smoke damper. It restricts the movement of smoke, works automatically from smoke detection and can be controlled remotely. In Europe, smoke control dampers are covered by EN 12101-8. The US model codes require leakage Class I or II.
• Russian terms. A fire damper may be normally open (closes in a fire), normally closed (opens in a fire) or double-acting. A smoke damper is normally closed and fitted in smoke exhaust shafts.

Equipment that has to survive the fire

For high-rise buildings, the Azerbaijani code AzDTN 2.7-9 requires smoke exhaust fans that keep working at 400 °C for 2 hours, and smoke dampers rated at least EI 60. Smoke must leave the facade at no less than 20 m/s, so that it is not drawn back into the air intakes. The imbalance between supply and exhaust air must not exceed 30%.

Testing

• NFPA 92 (2024 edition). Dedicated smoke control systems are tested at least every six months, nondedicated ones at least once a year. The tests measure airflow and pressure differences and include operation on standby power. Dedicated systems also run a weekly self-test through the smoke control panel.
• Russia. SP 7.13130 refers to GOST R 53300-2009 for acceptance and periodic tests of smoke ventilation.

In Azerbaijan

The official list of construction norms in force names AzDTN 2.12-2 for heating, ventilation and air conditioning. The code states that the Soviet SNiP 2.04.05-91* it replaced has had no legal force in Azerbaijan since September 6, 2017. Russian SP 7.13130, the European EN 12101 and NFPA 92 are not on the list. For high-rise buildings, AzDTN 2.7-9 (in force since September 30, 2025) adds the requirements above.

Common mistakes

• Pressurization without exhaust. Russian law has banned pressurization without smoke exhaust since 2022.
• Too much pressure. A stair door under too much pressure is too heavy to open, which is why every code in the table caps the pressure or the door opening force.
• Ventilation that keeps running. Without the interlock, general ventilation carries smoke to every area it serves.
• Designing to a withdrawn standard. EN 12101-6:2005 was replaced in 2022; its values no longer apply.
• Mixing up US codes. NFPA 90A and the International Mechanical Code place duct smoke detectors differently. Check which one the project follows.