Electrical, Acoustic, Transport and Safety Services: Illumination, Sound, Lifts, Fire, Automation and Specialised Buildings

Light is measured by luminous flux (lumen, lm), luminous intensity (candela, cd, lumens per steradian), illuminance (lux = lm/m², what a surface receives) and luminance (cd/m², what the eye sees from a surface). Luminous efficacy is lumens per watt. For a point source the inverse-square and cosine laws give E = I·cosθ ÷ d², where d is the distance and θ the angle from the surface normal. Worked example: I = 1,500 cd, a lamp 3 m above the working plane and a point 4 m to the side: d = 5 m, cosθ = 3/5 = 0.6, so E = 1,500 × 0.6 ÷ 25 = 36 lux.

For interior lighting the lumen method is E = N·F·UF·MF ÷ A, so N = E·A ÷ (F·UF·MF). Here E is the target illuminance, A the area, F the flux per luminaire, UF the utilisation factor (the fraction of lamp flux that reaches the working plane; it rises with room index and lighter surfaces) and MF the maintenance factor (lamp ageing and dirt). Worked example: a 12 m × 15 m room, E = 400 lux, F = 5,000 lm, UF = 0.6, MF = 0.8 needs N = 400 × 180 ÷ (5,000 × 0.6 × 0.8) = 72,000 ÷ 2,400 = 30 luminaires. Round the count up and place it on a regular grid.

• Luminaires are classed by light distribution: direct (nearly all light downward), semi-direct, general diffuse, semi-indirect and indirect (nearly all light up to the ceiling, which becomes the source: soft and glare-free but less efficient).
• Emergency and exit lighting: battery-backed or generator-fed fittings that switch on automatically on mains failure to light escape routes and exit signs.
• Museums and galleries: light-sensitive objects need low illuminance (of the order of 50 lux for the most sensitive), sources with little or no UV, no direct sun, and high-CRI accent lighting to show colour.
• Stage and auditorium: spot, flood, profile and Fresnel fittings with dimmers and a control desk; house lights dim for the performance.
• Sports lighting: high and uniform illuminance on the playing area, enough vertical illuminance for cameras, low glare, no flicker and instant switching.
• Façade, landscape, retail and hospital: cove, wall-washing and grazing light; control spill; shadow-free theatre luminaires with high CRI in hospitals. Control by occupancy sensors, daylight sensors and dimming; the energy code limits lighting power density.

Sound is a pressure variation in air. Sound intensity level SIL = 10 log₁₀(I ÷ I₀) dB with I₀ = 10⁻¹² W/m²; sound pressure level SPL = 20 log₁₀(p ÷ p₀) with p₀ = 20 μPa, and the two are equal in a free field. The threshold of hearing is about 0 dB and the threshold of pain about 120 dB. The audible range is about 20 Hz to 20 kHz, speech lies between about 125 Hz and 4 kHz, and dB(A) weights the level to match the ear's lower sensitivity at low frequency. A change of about 3 dB is just noticeable, and 10 dB sounds about twice as loud.

Decibels add on an energy basis: L = 10 log₁₀ Σ10^(Lᵢ/10). Two equal sources add 3 dB (60 dB + 60 dB = 63 dB), four equal sources add 6 dB and ten add 10 dB. When two levels differ by 10 dB or more, the louder one dominates (70 dB + 60 dB ≈ 70.4 dB). Never add decibels arithmetically. For a point source in a free field the level falls by 6 dB for each doubling of distance: L₂ = L₁ − 20 log₁₀(r₂ ÷ r₁); a line source such as a busy road falls by about 3 dB. Worked example: 80 dB at 5 m becomes 80 − 20 log₁₀ 4 = 80 − 12 = 68 dB at 20 m.

The absorption coefficient α of a surface is the fraction of incident sound energy that is not reflected, from 0 (fully reflecting) to 1 (an open window). Total absorption is A = Σ Sα in m² sabins. Reverberation time RT is the time for the sound to decay by 60 dB after the source stops, and Sabine's formula is RT = 0.161·V ÷ A with V in m³. Worked example: V = 750 m³; walls of 200 m² with α = 0.05, a ceiling of 150 m² with α = 0.60 and a floor of 150 m² with α = 0.10 give A = 10 + 90 + 15 = 115 m², so RT = 0.161 × 750 ÷ 115 = 1.05 s. Sabine suits rooms of low to moderate absorption; Eyring's formula, RT = 0.161·V ÷ [−S·ln(1 − ᾱ)], is better for very absorbent rooms.

• Porous absorbers (mineral wool, glass wool, acoustic tiles, carpets, curtains) absorb mid and high frequencies, and work better with an air gap behind them.
• Panel (membrane) absorbers, such as plywood or hardboard over an air space, absorb low frequencies.
• Resonant (Helmholtz) absorbers, a perforated or slotted panel over a cavity, absorb a narrow band set by the hole size and cavity depth.
• The noise reduction coefficient (NRC) is the average of α at 250, 500, 1,000 and 2,000 Hz.

Airborne sound insulation is measured by the transmission loss TL = 10 log₁₀(1 ÷ τ), where τ is the fraction of sound energy transmitted. By the mass law, each doubling of the surface mass of a single homogeneous partition, or of the frequency, raises TL by about 5 to 6 dB, so heavy walls insulate well and thin light ones poorly. A double-leaf wall with an air cavity, absorbent infill and no rigid ties between the leaves beats a single leaf of the same mass. Gaps matter more than mass: for a composite wall τ_avg = Σ(Sτ) ÷ ΣS. Worked example: a 10 m² wall of TL 40 dB containing a 1 m² door of TL 10 dB has τ_avg = (9 × 10⁻⁴ + 1 × 10⁻¹) ÷ 10 ≈ 1.01 × 10⁻², so TL ≈ 20 dB: the door has halved the wall's insulation in decibels.

• Impact (footfall) noise travels through the structure and is cured at source: a floating floor on a resilient layer, carpet or resilient finishes, and a suspended ceiling; extra slab mass helps only modestly.
• Structure-borne vibration from plant is isolated with anti-vibration mounts and flexible connections; duct noise needs silencers and lined ducts.
• Noise control follows source, path, receiver: quieter equipment first, then barriers, enclosures, planned adjacencies and sealed joints, and absorption in the receiving room last.
• Site planning helps: place noisy uses away from quiet ones, use buffer rooms, earth berms and solid barriers that break the line of sight to the source.

Auditorium design serves three aims: adequate loudness everywhere, clarity with even distribution, and a reverberation time suited to the use. Rules of thumb: allow about 3 to 5 m³ per seat for speech halls and more (about 7 to 10 m³) for music; rake the seating so every listener has a direct line of sight and sound; splay the side walls or use a moderate fan plan so that early reflections (within about 50 ms of the direct sound) reinforce it; put reflectors over the stage to send sound to the rear; keep balcony depth to no more than about twice its clear opening height; and put absorbers on the rear wall so late reflections do not return as echo. A reflection arriving more than about 50 ms after the direct sound (a path difference above about 17 m) is heard as an echo.

• Echo: a late, strong reflection, typically from a large flat or concave rear wall.
• Flutter echo: rapid repeated reflections between parallel hard walls, or floor and ceiling; cure by splaying or absorbing one surface.
• Sound foci and dead spots: concave domes and curved walls concentrate sound in a few places and starve others; use convex or diffusing surfaces.
• Sound shadow under deep balconies, room resonance in small rooms, and intrusion of outside and air-handling noise (use sound lobbies and silencers).

Electric traction lifts pull the car and a counterweight on ropes with a motor and sheave: geared for low and medium speed, gearless for high-speed tall buildings, and machine-room-less (MRL) types put the machine in the shaft; IS 14665 covers electric traction lifts. Hydraulic lifts push the car with a ram: low-rise, heavy loads, slow, and no overhead machine room. Every shaft needs a pit below and headroom above that grow with speed, plus guide rails, buffers and a safety gear tripped by an overspeed governor. Codes and bye-laws require lifts above a threshold height (commonly about 15 m), and tall buildings add a fire lift with its own power, a protected lobby and firefighter control; hospitals need bed or stretcher lifts.

Lifts are sized by traffic analysis of the up-peak (morning arrival) in offices. The round-trip time is RTT = 2H ÷ v + (S + 1) × t, where H is the highest reversal height, v the speed, S the number of stops and t the time per stop for doors and passenger transfer. The probable stops are S = N[1 − ((N − 1) ÷ N)^P] for N floors and P passengers per trip. Handling capacity HC = 300 × P ÷ RTT persons per 5 minutes per car, with P the average load (about 80% of rated capacity), and interval = RTT ÷ number of cars. Worked example: H = 36 m, v = 3 m/s, S = 6, t = 8 s: RTT = 24 + 7 × 8 = 80 s. With P = 8, one car has HC = 300 × 8 ÷ 80 = 30 persons per 5 minutes; three cars handle 90, with an interval of 80 ÷ 3 ≈ 26.7 s. Offices are designed for roughly 12 to 15% of the population in 5 minutes and an interval of about 30 s or less.

• Control types: down-collective, full-collective (stops for calls in both directions), group supervisory control (a processor assigns calls to cars) and destination dispatch (the passenger keys the floor in the lobby and is assigned a car).
• Group the cars together in the core near the main entrance: up to about four cars in a line, and larger groups in two facing rows with a lobby between them.
• Tall buildings split the height into low, mid and high zones with a bank for each, and use express lifts to sky lobbies, double-deck cars and shuttles to save core area.
• Capacity rises with car size, door width and speed; centre-opening doors are quicker, and speed rises with building height.

Escalators move people continuously at an incline of 30° (35° only for small rises at low speed) and about 0.5 m/s, with step widths of 600, 800 or 1,000 mm; the theoretical capacity rises in proportion to speed and width, and practical throughput is well below it. They suit short rises with heavy continuous flow in malls, stations, airports and stores, and are arranged crisscross or parallel. An escalator is generally not accepted as a means of escape, so stairs or lifts must sit beside it. Moving walks are horizontal or inclined up to 12°, and wheelchair ramps are no steeper than 1:12.

Fire needs fuel, oxygen and heat in a chain reaction; removing any one stops it. Fire safety rests on four ideas: prevent, detect and warn, contain (compartmentation with fire-rated walls, floors and doors, and fire dampers and fire stops in ducts and shafts) and extinguish and escape. Structural elements carry a fire-resistance rating in hours, and the National Building Code (Part 4, Fire and Life Safety) classifies buildings by occupancy and height, and buildings of about 15 m and above are commonly treated as high-rise for fire purposes.

Water-based systems start with hose reels (small-bore hoses for occupants' first-aid fighting), hydrants and risers. A dry riser is an empty pipe that the fire brigade charges through a ground inlet; a wet riser is permanently charged from a pump set and a terrace tank, with landing valves on each floor; yard hydrants serve the outside of the building. The pump house has a main pump (electric), a standby pump (diesel) and a small jockey pump that keeps the system pressurised and covers leaks. Stored water in the underground and terrace tanks is sized by flow × duration: a system designed for 1,800 L/min for 60 min needs 108,000 L (108 m³) set aside, apart from domestic water.

Automatic sprinklers open one head at a time: a glass bulb or fusible link releases at its rated temperature (bulb liquid colour: orange 57°C, red 68°C, yellow 79°C, green 93°C), and only the heads near the fire discharge. Choose a rating well above the highest normal ambient. Systems are wet pipe (pipes full of water; the common choice), dry pipe (pipes hold air; for freezing or unheated spaces), pre-action (water enters only after a detector confirms fire; data centres, museums, archives) and deluge (all heads open, released by detection; hangars and chemical plants). Other fixed systems are water spray or mist, foam and gaseous (CO₂, clean agents such as HFC-227ea, or inert gases) for rooms where water would do harm.

• At least two separate exits from every floor in most occupancies, remote from one another; travel distance to the nearest exit is limited by occupancy, and is shorter for sleeping and institutional uses.
• Exit stairs sit in fire-rated enclosures with self-closing doors that open in the direction of escape and lead to ground level and open space; no lift or escalator counts as an exit.
• In tall buildings, pressurised stairs and smoke lobbies keep smoke out of the escape route; exit signs, emergency lighting, a fire alarm with voice evacuation and a fire command centre guide and control the evacuation.
• Refuge areas in high-rise buildings and horizontal exits into an adjoining fire compartment in hospitals serve people who cannot use stairs quickly; fire tenders need approach roads and open space around the building.

A building automation system (BAS) is the building's control network. Sensors (temperature, humidity, CO₂, occupancy, light, pressure, flow) feed controllers (DDC or PLC), which drive actuators (valves, dampers, drives, relays) in HVAC, lighting and pumps. Communication uses protocols such as BACnet, Modbus, LonWorks, KNX and DALI (for lighting); open protocols let equipment of different makers work together and avoid vendor lock-in. Typical functions are time schedules, set-point and reset control, optimum start, demand-controlled ventilation by CO₂, night purge, lighting control by occupancy and daylight, and alarm handling.

A building management system (BMS) sits above the BAS. Its front end (server and operator workstations) supervises, trends, raises alarms, schedules and reports, and manages energy metering, maintenance and the history that supports energy audits and green-rating evidence. An integrated BMS (IBMS) also links the fire alarm, access control, CCTV, lifts, public address and power systems on one platform, so one event, such as a fire alarm, triggers a coordinated response: lifts recalled to the ground floor, stair pressurisation on, access doors released. The terms overlap in everyday use: the BAS controls, the BMS supervises and integrates.

• CPTED (crime prevention through environmental design): natural surveillance, natural access control, territorial reinforcement and good maintenance.
• Layered security: deter, detect, delay, respond; for blast threats add stand-off distance and structures that avoid progressive collapse.
• Fail-safe locks release on fire alarm or power loss, as escape doors must; fail-secure locks stay locked, and suit store rooms and cash areas that are not on an escape route.
• Building safety also covers earthing and lightning protection, gas-leak detection, lift safety devices, smoke control and structural safety.

Hospitals are life-critical buildings that run round the clock. Pressure cascades keep air flowing from clean to less clean areas: operating theatres and protective-isolation rooms are positive, airborne-infection isolation rooms negative, with HEPA-filtered air, high air-change rates and controlled temperature and humidity in theatres. Medical gas pipelines carry oxygen, nitrous oxide, medical air and vacuum to bedhead and theatre outlets, with alarms and standby manifolds. Essential power comes from DG sets with automatic changeover, with UPS and an isolated power supply with equipotential earthing in theatres and critical care. Water use per bed is high; clinical areas use hot water and elbow- or sensor-operated taps; effluent is treated and biomedical waste is segregated into colour-coded bags (yellow, red, white and blue categories). Patients cannot use stairs quickly, so fire compartments with horizontal exits, and bed or stretcher lifts, are provided.

Indoor sports stadiums and arenas are large, tall and crowded volumes. Air is supplied low into the seating bowl at low velocity so that only the occupied zone is conditioned; ice rinks need refrigeration and dehumidification, and swimming halls need dehumidification and vapour control to avoid condensation on the roof. Lighting needs high, uniform illuminance, enough vertical illuminance for television, low glare, no flicker and instant switching. A large hard volume has a long reverberation time, so absorbent roof decks and a zoned, delayed loudspeaker system are needed for clear speech. For crowd safety there are short travel distances, many exits and vomitories sized for crowd flow, smoke reservoirs and high-level extraction, beam or aspirating detection, and a command room. Large roofs call for high-capacity or siphonic roof drainage and storm-water attenuation, and toilets are sized for the interval peak.

High-rise buildings multiply every service by height. Water supply is zoned with intermediate tanks, transfer pumps and pressure-reducing valves so that static pressure stays within limits, with separate fire-water tanks. Electrical risers, busbar trunking and substations at intermediate floors serve the height, and emergency power is given to fire lifts, pressurisation fans and escape lighting. Plant rooms sit on mechanical floors; plate heat exchangers break the static head of chilled-water risers; the stack effect drives air and smoke movement in shafts, so stairs are pressurised. Lifts are zoned in banks with sky lobbies, plus a fire lift. Fire safety adds wet risers with zoned pumps, sprinklers, refuge floors, a fire command centre, voice evacuation and fire-stopped shafts at every slab. Drainage stacks are vented and offsets avoided, and refuse chutes are fire-rated. Lightning protection, aviation obstruction lights where the aviation authority requires them, and powered façade-maintenance access complete the services.