COMMENTARY ON CLAUSE 17

Vertical Escape Design Considerations:

a) Vertical Escape:

Typically involves transitioning from horizontal escape to a place of safety, often a protected staircase.

b) Stair Design Impact:

· Influences evacuation speed; fear of accidents can slow movement.

· Effective lighting, handrails, and correct riser-to-tread ratio enhance speed and safety.

c) Accident Prevention:

· Falls often result from incorrect riser-to-tread ratio; even a 5 mm difference can be dangerous.

· Marked step edges improve safety.

d) Stair Width and Flow Rate:

· Widths must accommodate the flow rate for simultaneous evacuation.

· Fire floor occupants typically enter first; potential congestion from upper floors must be considered.

e) Disabled People:

Specific recommendations for vertical escape are detailed in section 17.8.

17.1 General

The design for vertical means of escape should meet the performance recommendations for horizontal escape (see Clause 16), for each storey exit in a building.

17.2 Design of escape stairs

17.2.1 General

a) Only Staircase:

Must be of limited combustibility unless the building is 2-3 storeys and has risk profile A1, A2, or B1.

b) Basement:

Applies to escape stairs within basement storeys.

c) Height:

Applies to stairs serving storeys with floor levels over 18 m above ground/access level.

d) External Stairs:

Required for external stairs, except those connecting ground level to a floor or flat roof within 6 m.

e) Fire-Fighting Stairs:

Must always be constructed of materials of limited combustibility.

17.2.2 Enclosure of escape stairs

a) Protected Stairs:

Should be within a fire-resisting enclosure.

b) Unprotected Stairs:

Can be part of an internal route to a storey or final exit if an appropriate risk assessment deems it acceptable.

NOTE Additional enclosure measures might be necessary if the protected stairway is also a protected shaft or a fire-fighting shaft.

17.2.3 External walls of protected stairways

1. Projection or Recess:

Applies when a protected stairway projects beyond, is recessed from, or forms an internal angle of ≤135° with the building's external wall.

2. Separation Distance:

There should be at least 1,800 mm between unprotected areas in the building's external enclosure and the stairway's enclosure. (see Figure 15)

17.2.4 Added protection to stairs

a) Protected Lobby/Corridor or Pressure Differential System Requirements:

● Single Escape Stair:

Required if it's the only stair serving a building with multiple storeys above or below ground level.

● Height:

Required if serving a storey over 18 m in height.

● Phased Evacuation:

Necessary in buildings designed for phased evacuation.

● Stair Width Calculation:

Needed if stair width isn't based on discounting one stairway.

b) Provision Requirements:

● Protected lobbies or corridors should be provided at all levels, except the top storey and include all basement levels.

● A protected lobby is also needed between an escape stairway and areas of high fire risk.

17.2.5 Exits from protected stairways

Every protected stairway should discharge directly to a final exit, or by way of a protected exit passageway to a final exit.

Figure 15 External protection to protected stairways – Configurations of stairs and external wall

17.2.6 Separation of adjoining stairways

Where two protected stairways are adjacent, either they, and any protected exit passageways linking them to final exits, should be fire-separated, or both stairways should be discounted in any calculations (see 17.3.2).

17.2.7 Final exits from stairs

a) Exit Route Requirements:

● Width: The exit route from a stairway must be at least as wide as the stair itself.

● Shared Routes: If the exit route serves both ground and/or basement storeys, the width may need to be increase.

b) Protected Stairway Discharge:

● Direct Discharge: Should lead directly to a final exit.

● Protected Exit Passageway: Can lead to a final exit via a protected passageway.

● Fire Resistance: Any protected exit passageway must have the same fire resistance and lobby protection as the stairway it serves.

17.2.8 Single steps

Single steps can cause falls and should be avoided on escape routes. Where such steps are unavoidable, they should be prominently marked.

NOTE Ramps can often be used to avoid single steps.

17.2.9 Helical stairs and spiral stairs

a) Design Standard:

Must be designed according to BS 5395-2.

b) Usage Limitation:

Should not be the sole means of escape.

17.3 Number of escape stairs

17.3.1 General

a) Horizontal Escape Routes: Consider constraints on their design.

b) Single Stair Acceptability: Evaluate if a single stair can suffice. (see 17.3.3)

c) Independent Stairs: Assess need in mixed occupancy buildings. (See 17.3.4

d) Adequate Width: Ensure sufficient width for escape, considering the potential discounting of a stair due to fire or smoke. (see 17.4.1) (see 17.3.2).

NOTE In larger buildings, it might be necessary to provide access for the fire and rescue service, in which case some escape stairs might also need to serve as fire-fighting stairs (see 20.2.1).

17.3.2 Discounting of stairs

a) Discounting Stairs:

Assume one stairway might be unavailable due to fire or smoke when determining the aggregate capacity. Discount each stair in turn to ensure remaining stairways can accommodate all occupants.

b) Exceptions to Discounting:

c) Protected Lobbies:

If stairways are accessed through protected lobbies on each storey (excluding the topmost), discounting is unnecessary.

d) Smoke Control System:

If stairways are protected by a smoke control system per BS EN 12101-6:2005.

e) Sprinkler System:

If the building is equipped with a sprinkler system.

17.3.3 Single escape stairs

Provided that independent escape routes are not necessary from areas put to different uses (see 17.3.4), a building (or part of a building) may be served by a single escape stair in the following situations:

a) a basement which is allowed to have a single escape route in accordance with 16.3.3;

b) a building that has no storey with a floor level more than 11 m above ground level, and in which every storey is allowed to have a single escape route in accordance with 16.3.3.

NOTE See 17.2.4a) for lobby protection of single stairways.

17.3.4 Mixed-use buildings

a) Risk Assessment: Assess the impact of one use (e.g., a shop or office) on another (e.g., residential or hotel) in the same building.

b) Separate Escape Routes: Determine if completely separate escape routes are needed for each use.

c) Common Escape Route Protection: Evaluate alternative protective measures for common escape routes.

17.4 Width of escape stairs

17.4.1 Absolute minimum width

a) Measuring Escape Stair Width:

● Measured as the clear width between walls or balustrades, at the narrowest point up to 1,500 mm above pitch line.

b) Width Requirements:

c) Minimum Width:

● Not less than the width of exits providing access to the stair.

● At least 1,000 mm for downward travel.

● At least 1,200 mm for upward travel.

d) Consistent Width:

Must not narrow at any point on the way to a final exit.

e) Maximum Width:

● Should not exceed 1,400 mm if the vertical extent is over 30 m, unless a central handrail is provided.

● If a central handrail is present, there should be at least 1,000 mm of space on each side.

● Each side of the central handrail should be assessed separately for stair capacity.

NOTE 1 Handrails and strings which do not intrude more than 100 mm into this width may be ignored.

NOTE 2 For door widths for simultaneous evacuation, see 17.4.2.

17.4.2 Simultaneous evacuation

NOTE See also 12.2.1.

a) Escape Stair Width Requirements:

b) Capacity for Emergency:

Must accommodate the number of people using the stair in an emergency.

c) Simultaneous Evacuation:

· Stairs should allow for evacuation of all floors at once and quick exit for those on the fire floor.

· Required for all stairs serving basements.

d) Minimum Width:

· Should be at least the greater of:

· Dimensions specified in 17.4.1.

· Dimensions given in Table 13 for the appropriate risk profile and number of floors.

· Additional fire protection measures may modify these requirements

Table 13 Minimum width of escape stairs for simultaneous evacuation

Risk profile Minimum width of stair per person served over total number of floors served A)
	1 floor	2 floors	3 floors	4 floors	5 floors	6 floors	7 floors	8 floors	9 floors	10+ floors
A1	3.90	3.40	2.95	2.45	2.15	2.00	1.80	1.70	1.50	1.40
A2	4.50	3.80	3.25	2.75	2.45	2.20	2.00	1.90	1.70	1.60
A3	5.40	4.60	4.00	3.50	3.10	2.80	2.60	2.30	2.10	2.00
A4 B)	—	—	—	—	—	—	—	—	—	—
B1	4.20	3.60	3.10	2.60	2.30	2.10	1.90	1.80	1.60	1.50
B2	4.80	4.00	3.40	2.90	2.60	2.30	2.10	2.00	1.80	1.70
B3	7.00	6.00	5.30	4.60	4.20	3.70	3.40	3.10	2.80	2.60
B4 B)	—	—	—	—	—	—	—	—	—	—
C1 4.20		3.60	3.10	2.60	2.30	2.10	1.90	1.80	1.60	1.50
C2 4.80		4.00	3.40	2.90	2.60	2.30	2.10	2.00	1.80	1.70
C3 B) 7.00		6.00	5.30	4.60	4.20	3.70	3.40	3.10	2.80	2.60
C4 B) —		—	—	—	—	—	—	—	—	—

Note: The widths of stairs have been calculated on the assumption that all floors are evacuating simultaneously. This is conservative, as the occupants on the fire floor are likely to move more quickly than on the other floors.

A) If the stair and a storey exit at the final exit level share a common final exit door then the total number of floors served by the stair should include the storey at final exit level (see also 15.6.6e) and Figure 6)

B) See Table 4

17.4.3 Phased evacuation

COMMENTARY ON 17.4.3

a) Advantages: Allows for narrower stairs and reduces disruption in large buildings, but may not be suitable for all buildings.

b) Minimum Width: See also 12.2.2.

● Aggregate width of escape stairs should be at least the greater of:

● Dimensions specified in 17.4.1.

● Dimensions given in Table 13 for the appropriate risk profile and maximum capacity on any two floors.

● Additional fire protection measures may alter these requirements.

17.4.4 Mixed-use buildings

a) Apply Higher Value:

Use the more onerous width value from Table 13 that matches the highest risk profile present in the building.

b) Exception:

If occupants with different risk profiles use the stair at different times, the highest value should still be applied.

17.5 Basement stairs

COMMENTARY ON 17.5

a) Separate Stair for Basement:

Avoid using an escape stair from an upper storey to serve a basement; use a separate protected stair for the basement.

b) Smoke Control System Exception:

If the stair is protected by a smoke control system (BS EN 12101-6:2005), it can continue into the basement if users are guided to the final exit.

c) Small Buildings Exception:

In buildings where the top floor is ≤11 m above ground or with ≤3 storeys above ground:

● Fire-Resisting Lobby: Provide a fire-resisting ventilated lobby at basement level.

● Fire-Resisting Separation: Separate basement and upper storeys with fire-resisting construction and an FD 30S self-closing door at ground floor level.

d) Multiple Stairs:

Only one stair from upper storeys needs to terminate at ground level. Other stairs may connect to the basement if there is a ventilated protected lobby or corridor at each basement level. The lobby should meet requirements of 27.5.

17.6 Protected stairs

a) Sanitary Accommodation:

Allowed if not used as a cloakroom; can include a gas water heater or sanitary towel incinerator but no other gas appliances.

b) Lift Well:

Permitted unless the stair is a fire-fighting stair.

c) Reception Desk/Inquiry Office:

Allowed at ground/access level if not the only stair serving the building; must be ≤10 m².

d) Cupboards:

Allowed if enclosed with fire-resisting construction and not in the only stair serving the building.

e) Gas Service Pipes/Meters:

Permitted.

f) Service Shafts:

Can be accessed from a protected stairway if enclosed with fire-resisting construction and FD 30S doors, and if the stair is not the only one serving the building.

NOTE Examples of such facilities are:

17.7 External escape stairs

a) Internal Escape Stair:

At least one internal escape stair must serve every part of each storey (excluding plant areas).

b) Single Access Stair:

If only one access stair is provided, it can be external if the following conditions are met:

● Fire-Resisting Doors:

All doors to the external stair must be fire-resisting and self-closing, except at the head of stairs leading downward with only one exit.

● Fire-Resisting Walls:

External walls within 1,800 mm horizontally and 9 m vertically below the stair flights and landings must be fire-resisting. This can be reduced to 1,100 mm above the top level of the stair if not leading up from a basement.

● Protection of Escape Route:

Any part of the building within 1,800 mm of the escape route to safety must be fire-resisting.

● Fire-Resisting Glazing:

Glazing in fire-resisting areas must also be fire-resisting, fixed shut, and meet criteria for integrity and insulation.

● Weather Protection: Stairs with vertical extent >6 m must be protected from adverse weather conditions.

NOTE A full enclosure is not necessary. The extent of enclosure needed depends on the location of the stair and the degree of protection given to the stair by the building itself. Trace heating is acceptable but needs to be maintained throughout the life of the building and be treated to the same standard as emergency escape lighting and provided with thermostatic control to operate in cold weather.

Figure 16 Fire resistance of areas adjacent to external stairs (1 of 2)

Figure 16 Fire resistance of areas adjacent to external stairs (2 of 2)

17.8 Methods of vertical escape for disabled people

COMMENTARY ON 17.8

a) Preferred Methods:

● Horizontal Evacuation: Move to the outside of the building or another fire compartment.

● Evacuation Lift: Use if available and operational.

b) Alternative Measures:

● Carrying: If preferred methods are unavailable, it may be necessary to carry individuals with limited mobility up or down stairs.

● Combination Approach: Use a mix of structural provisions (e.g., lifts, refuge areas, ramps) and management procedures (e.g., assisted escape).

c) General Expectation:

● Most disabled people should be able to reach a place of relative safety with the support provided.

● Some, such as wheelchair users, may need additional assistance as they cannot negotiate stairs unaided.

17.8.1 General

A strategy should be designed to enable a flexible response to different situations.

17.8.2 Escape using a lift

If an evacuation lift is provided, it should be in accordance with Annex G.

NOTE See also 15.8.

Non-Evacuation Lifts: Should not be used for general evacuation.

Use for Disabled Evacuation: Allowed if the recommendations in 45.9 are met.

17.8.3 Evacuation by stairs

a) Staircase Design: Should align with the adopted evacuation strategy for disabled people.

b) Management Plan: Must specify the procedure for carrying disabled people up or down stairs.

c) Staff Training: Identify and train staff to assist in conveying disabled people up and/or down the evacuation stairs.

NOTE See also 45.10.

17.8.4 Refuges

COMMENTARY ON 17.8.4

a) Assists Disabled Evacuation: Helps manage the escape of disabled people.

b) Prevents Hindrance: Ensures the evacuation of disabled people does not obstruct other building users.

See also 45.8.

If a refuge is provided, it should be in accordance with Annex G.

17 Vertical means of escape