HKIE Professional Assessment - Fire Discipline cheat sheet

Combustion requires fuel, oxidant, heat and an uninhibited chain reaction; removing any one of the four (the fire tetrahedron) extinguishes flaming combustion.

Heat release rate per unit area: HRRPUA = HRR/A_fire; a growing fire is often modelled as t-squared, Q = αt², with α (kW/s²) slow 0.0029, medium 0.012, fast 0.047, ultrafast 0.19.

Flashover in a compartment is commonly correlated with upper-layer gas temperature near 600 °C or radiant heat flux at floor level of about 20 kW/m²; a post-flashover fire is fuel-surface-controlled.

Ventilation-limited burning: air mass flow through an opening m ≈ 0.5·A_o·√H_o (kg/s, A_o in m², H_o in m); stoichiometric ratio for typical fuels is roughly 1.3–3 kg air per kg fuel.

Smoke is buoyant because hot products are less dense than ambient air; the pressure differential across a compartment boundary drives smoke spread and is typically a few pascals to tens of pascals.

Compartment fire stages: incipient, growth, flashover, fully developed, decay; detection and egress design must be matched to the stage the design fire has reached.

Radiation from a flame or hot layer: q'' = εσT⁴ for a blackbody and q'' = φ·ε·σ·(T⁴−T_o⁴) for incident flux with configuration factor φ.

Smoke layer descent can be estimated by the mass balance of combustion products accumulating under a ceiling; a descending hot layer reduces tenability before temperatures become intolerable.

Means of escape is designed around travel distance, exit width and number of exits; exit capacity is normally expressed in units of 5 mm per person for level surfaces, with discounting of the widest exit when multiple exits exist.

Fire resisting construction is rated by stability, integrity and insulation (e.g. 60/60/60 minutes); the required period depends on building height, occupancy and compartment size.

Compartmentation limits fire size and smoke spread; compartment area and volume limits are set by the applicable code and may be relaxed by a performance-based alternative with justification.

Passive protection includes fire-rated walls, floors, doors, dampers, penetration seals and protected shafts; active protection includes detection, alarm, sprinklers, drenchers and smoke control.

Protected lobby and staircase pressurisation protect escape routes; a staircase serving a high-rise must normally be approached through a protected lobby with self-closing fire doors.

Where a building exceeds the code's prescriptive limits (height, area, travel distance), an alternative approach with fire engineering justification and authority acceptance is required.

Dead-end travel, inner rooms, and single-direction escape must be checked against code maxima; the escape route must remain available for the duration of the occupant evacuation.

Fire resistance of structural elements must be maintained to the required period including protection of steel (intumescent coating, board, concrete encasement) and connections.

Sprinkler design density and operating area are selected from the occupancy hazard class; the design point is the most hydraulically remote operating sprinkler head.

Sprinkler K-factor relates flow to pressure: Q = K√P; common K-factors are 80 (metric) for standard spray and 115 or 161 for higher-flow heads.

Gaseous clean-agent systems (e.g. FM-200, Novec 1230, IG-541) are designed to a minimum design concentration for the fuel and hold time; room integrity (door fan test) and enclosure leakage are critical.

Water-mist systems use fine droplets for cooling and oxygen displacement; they are not interchangeable with sprinklers and require listing for the specific application and hazard.

Detection technology selection: ionisation is sensitive to flaming fires, optical (photoelectric) to smouldering smoke, heat detectors to fast-flaming fires, and beam/aspirating systems for large or high spaces.

Alarm and control philosophy: detection triggers alarm, alarm triggers cause-and-effect matrix actions (plant shutdown, damper closure, door release, pressurisation, suppression release) with staged or double-knock logic where required.

Pre-action and deluge systems require a detection signal before water is admitted; dry-pipe systems rely on air pressure and have a longer water delivery time than wet systems.

Standby power, battery autonomy and monitored circuits are required for detection and alarm systems so that they remain operational on mains failure for the specified duration.

Performance-based design follows a structured process: define fire safety objectives, identify fire scenarios, select design fires, analyse with models, compare against acceptance criteria, and document uncertainty.

Design fire selection must consider fuel load, fuel arrangement, ignition likelihood, ventilation conditions and active system reliability; a design fire is not the worst case but a justified credible case.

Fire models: zone models (e.g. two-zone) assume uniform upper and lower layers; CFD field models resolve the flow field and are used where geometry or smoke control demands it.

Egress analysis compares available safe egress time (ASET) with required safe egress time (RSET); RSET = detection + pre-movement + travel time, with safety margin.

Tenability criteria commonly include visibility, temperature, radiant heat flux, and toxic gas (CO, CO₂, HCN) exposure; criteria must be justified and applied consistently.

Risk assessment methods include qualitative (checklists, HAZOP), semi-quantitative (risk matrices) and quantitative (event tree, fault tree, frequency-consequence); the method must suit the decision.

Sensitivity and uncertainty analysis is mandatory for any performance-based submission: vary key inputs (α, soot yield, leakage, door status) and show the design remains acceptable.

Smoke control design uses either smoke reservoir and natural venting or mechanical extract; the design must account for make-up air and the pressure regime created by the fans.

The Buildings Ordinance (Cap. 123) governs construction, alteration and use of buildings; the Building Authority administers it through the Buildings Department.

The Fire Safety (Buildings) Ordinance (Cap. 572) imposes fire safety improvements on composite and domestic buildings constructed before specified dates, covering fire service installations, means of escape and fire resisting construction.

The Fire Services Ordinance (Cap. 95) and its subsidiary regulations govern fire service installations and equipment, with the Fire Services Department as the authority for acceptance and licensing.

The Code of Practice for Minimum Fire Service Installations and Equipment and Inspection, Testing and Maintenance sets the required installations and maintenance regime; the Code of Practice for Fire Safety in Buildings addresses means of escape, fire resisting construction and related design.

Licensing regimes for specified commercial premises (e.g. restaurants, karaoke, hotels) require a fire safety certificate or compliance with the Fire Safety (Commercial Premises) Ordinance (Cap. 502) requirements.

Submission and approval flow: building plans, fire service installation plans, and occupation permits each require separate approval; FSI acceptance testing precedes occupation.

Registered fire service installation contractors must be employed for installation, and periodic inspection, testing and maintenance by registered personnel is required to keep the FSI certificate valid.

Any departure from the codes requires an alternative approach with fire engineering justification submitted to and accepted by the Building Authority and/or Fire Services Department, as applicable.

Hydrant/hose reel systems: street hydrants and internal hydrants are supplied from a dedicated fire service tank and pump set; the required flow and pressure are set by the code and confirmed by hydraulic calculation.

Fire pumps are typically duty/standby with a jockey pump to maintain pressure; pump starting is triggered by pressure drop and the pump must deliver the design flow at the design pressure at the most remote outlet.

Fire service water tanks must hold the specified capacity for the required duration; the effective capacity excludes the volume below the suction outlet and any unusable reserve.

Hose reels are for first-aid use by occupants; hydrants and landing valves are for Fire Services Department use, with landing valves at each floor in high-rise buildings.

Smoke control: staircase and lobby pressurisation must maintain a positive pressure differential across closed doors while limiting door-opening force; relief dampers and leakage paths are part of the design.

Emergency lighting and exit signs must provide the specified illuminance and duration on failure of normal supply; battery and generator-backed systems need periodic discharge testing.

Sprinkler and hydrant pumps require a dedicated power supply, and the fire service installation must remain operational during a mains failure for the specified period.

Commissioning and acceptance testing includes flow tests, pressure tests, alarm and cause-and-effect verification, and documentation retained for the FSI inspection regime.

Fire investigation follows a systematic method: secure the scene, document before disturbing, examine the origin and cause, and test hypotheses against physical evidence.

Burn patterns (V-patterns, alligatoring, char depth, spalling, melting points) indicate direction and intensity but must be interpreted together; no single indicator is conclusive.

Origin determination uses the lowest point of burning, greatest damage, and the fire's direction of travel; multiple origins suggest deliberate ignition.

Accelerant detection uses laboratory analysis (e.g. GC-MS) of debris; field indicators such as pour patterns are supporting evidence only, not proof.

Post-fire structural assessment must consider reduced section, loss of strength at elevated temperature, and residual capacity; concrete spalling and steel distortion require engineering evaluation before reoccupation.

Forensic reporting must distinguish observation, interpretation and opinion, and be suitable for use in litigation or a coroner's inquest.

Electrical fire causes include overload, poor connections, arcing and insulation failure; evidence must be preserved and examined before removal of the wiring.

Fire modelling can support or challenge a hypothesis but is not evidence by itself; the model's assumptions and inputs must be defensible in a forensic context.

Professional engineers owe duties to the public, the client and the profession; competence, honesty and disclosure of conflicts of interest are core obligations.

Signing and certifying work implies personal responsibility for the design; a certifying engineer must have actually reviewed and be able to defend the design.

Safety management systems use hazard identification, risk assessment, control measures and review; construction sites require a safety plan and method statements for hot work and fire-risk activities.

Project delivery: define scope, interfaces and acceptance criteria early; fire safety interfaces with architecture, structure, MEP and operations, and must be coordinated, not added at the end.

Change control: any change to layout, occupancy or fuel load after approval must be assessed for its effect on the fire strategy and re-submitted where required.

Records and handover: as-built drawings, O&M manuals, commissioning records and maintenance schedules are part of the deliverable and underpin the FSI inspection regime.

Ethical reporting: if a design is found non-compliant or unsafe, the engineer must report it promptly to the responsible party and not conceal it.

Continuing professional development and knowledge of current codes and amendments are expected; outdated code knowledge is a competence risk.