Fire engineering glossary

A

Accountable person

The dutyholder responsible for a higher-risk building in occupation. Holds the golden thread, prepares the safety case report and engages residents. Where there is more than one, a principal accountable person is identified. More

ADB

Approved Document B. The guidance supporting Requirement B of Schedule 1 to the Building Regulations in England. Volume 1 covers dwellings, Volume 2 buildings other than dwellings. More

Alternative escape route

A route sufficiently separated from another route, by direction and by construction, that a fire affecting one will not affect the other.

ASET

Available safe egress time. The time from ignition until conditions in the space become untenable for occupants. More

C

Cavity barrier

A construction provided to close a concealed space against the passage of flame and smoke, or to restrict its movement within the space. The most common defect found when external walls are opened up. More

Compartmentation

Division of a building by fire-resisting construction so that a fire in one part does not spread to another. What a stay-put strategy depends on entirely. More

Competent person

Someone with the skills, knowledge, experience and behaviours to carry out the work. Under the Building Safety Act regime, competence is declared and must be evidenced, and it attaches to a named individual.

D

Dead end

A part of an escape route from which escape is possible in one direction only. Travel distance limits in a dead end are substantially shorter than where escape is available in more than one direction. More

Departure

A design decision that does not follow the guidance being used. Legitimate, and normal on complex buildings, but every one must be identified and justified in writing. Unjustified departures are a leading cause of Gateway 2 failure. More

Direct distance

The straight-line distance from a point to the nearest storey exit, disregarding walls and partitions. Conventionally taken as two thirds of the permitted travel distance where the layout is not yet fixed. More

Dutyholder

A role with defined statutory duties under the Building Safety Act regime: client, principal designer, principal contractor, designer, contractor. Each must be competent and must cooperate.

E

EI

A fire resistance classification under BS EN 13501-2 covering integrity (E) and insulation (I), for a stated period in minutes. Applies to non-loadbearing elements. More

Enclosing rectangle

The smallest rectangle enclosing all the unprotected areas on an external wall. The tabular space separation method works from this rectangle and the percentage of it that is unprotected. More

Euroclass

The reaction to fire classification system of BS EN 13501-1, running A1, A2, B, C, D, E, F, with additional s ratings for smoke production and d ratings for flaming droplets.

EWS1

External Wall System form. A lending and valuation instrument, not an engineering standard. Increasingly issued on the back of a PAS 9980 appraisal rather than instead of one. More

F

FD30 / FD60

Fire door ratings, giving the integrity period in minutes. An S suffix indicates smoke control. The rating belongs to the tested assembly (leaf, frame, seals, hinges, closer and gaps), not to the door leaf alone. More

Fire and emergency file

The fire safety information submitted with a Gateway 2 application and maintained thereafter. In practice, the fire strategy and the fire strategy drawings. More

Fire resistance

The ability of an element to fulfil its required functions for a stated period when exposed to fire, classified under BS EN 13501-2 as R for loadbearing capacity, E for integrity and I for insulation. More

Fire strategy

The document that sets out how a building achieves fire safety: the design basis, the standard being used, the provisions made, and the justification for every departure. More

FRAEW

Fire risk appraisal of external wall construction, carried out to PAS 9980:2022. Produces a reasoned risk rating rather than a pass or fail. More

G

Gateway 1

The planning stage of the Building Safety Act regime, where fire safety matters relevant to planning are considered for higher-risk buildings.

Gateway 2

Building control approval for a higher-risk building, granted by the Building Safety Regulator. Work cannot start until it is granted. More

Gateway 3

Completion certificate stage. The building cannot be occupied until it is granted, and the golden thread transfers to the accountable person. More

Golden thread

The requirement that the information needed to manage a higher-risk building's fire and structural safety is accurate, current, accessible and transferable, from design through occupation. More

H

Higher-risk building

In England, a building at least 18 m in height or with at least seven storeys, containing at least two residential units, or a care home or hospital meeting the same height test. More

M

Means of escape

The structural means by which a safe route is provided for people to travel from any point in a building to a place of safety, without assistance. More

N

Notional boundary

A boundary drawn between two buildings on the same site so that space separation can be assessed for each. It does not have to sit at the mid-point. More

O

Occupant capacity

The number of people a room, storey or building is designed to hold, derived either from a stated design occupancy or from floor space factors. More

P

PAS 9980

Publicly Available Specification 9980:2022, the code of practice for fire risk appraisal of external wall construction on existing multi-storey residential buildings. More

PD 7974

The series of Published Documents supporting BS 7974, containing the calculation methods for a performance-based fire safety engineering analysis. Parts 1 to 7. More

Protected stairway

A stair discharging to a final exit, together with any protected lobbies or corridors between it and the exit, enclosed with fire-resisting construction.

R

REI

A fire resistance classification covering loadbearing capacity (R), integrity (E) and insulation (I) for a stated period. Required where the element carries load. More

Relevant boundary

The boundary a building is assessed against for space separation. May be the site boundary, the centre line of an adjoining road, railway, canal or river, or a notional boundary. More

RSET

Required safe egress time. Detection time plus alarm time plus pre-travel time plus travel time, per PD 7974-6 equation (2). PD 7974-6 gives pre-travel time at two percentiles, so RSET is properly a range. The margin of safety is ASET minus RSET, and the acceptable margin is agreed at the qualitative design review rather than settled afterwards. More

S

Safety case report

The document by which an accountable person demonstrates that the fire and structural risks in an occupied higher-risk building are being properly managed.

Simultaneous evacuation

An evacuation strategy in which the whole building leaves at once. Applied as an interim measure where a defect means a stay-put strategy cannot be relied on, with significant consequences for stair capacity. More

Space separation

The provision of distance between a building and its relevant boundary so that radiation from a fire does not ignite the neighbouring building. Assessed against a 12.6 kW/m² criterion. More

Stay put

An evacuation strategy in which residents not directly affected by a fire remain in their flats, relying on compartmentation to contain it. Valid only where the compartmentation is intact and demonstrably so.

Storey exit

An exit from a storey directly to a final exit or to a protected stairway. Travel distance is measured to the nearest storey exit. More

T

Travel distance

The actual distance a person must walk from any point to the nearest storey exit, following the route around fixed obstructions. More

U

Unprotected area

Any part of an external wall that is not fire-resisting: openings, windows, doors, and wall with less than the required fire resistance. Combustible external surfaces above a specified thickness also count, typically at a reduced rate. More

V

View factor

The geometric fraction of radiation leaving a surface that reaches a given receiving point. The core of a BR 187 space separation calculation. More

W

Waking watch

An interim measure in which staff patrol a building to raise the alarm where the evacuation strategy cannot be relied on. Expensive to run and normally replaced by a common alarm system as soon as one can be installed. More