Introduction
Capital Dhaka City, having a rate of urbanization of 30% and 50% respectively in 1974 and 1991, has impacted on the growth of multi-storeyed shopping complexes. Notwithstanding their encroachment into residential areas of the city, this new trend for obvious reasons is dependent on mechanized services, such as lift, escalators, central air conditioning system. In these introvert planned multi-storeyed shopping complexes the means of vertical circulation becomes very vital in terms of safety, security and efficiency.

History of commercial growth of Dhaka City
In the 9th C. AD Dhaka was a small market town lying between the Dolai Khal and Buriganga River near present Bangla Bazaar during the reign of Sena kings of Vikrampur.

On the arrival of the Muslim rulers commercial growth increased, and the city became to be known as 'Bahanna Bazaar-o-Tippanna Goli' (52 markets and 53 lanes).

After its establishment as the Mughal provincial capital in 1610 with the name Jahangirnagar, Dhaka attracted foreign individual merchants as well as organised European companies.

The Afghans, the Persians, the Armenians, the Dutch, the Greeks, the French, the Portuguese and the English all had trade and commerce links with Dhaka.

Commodities like the famous muslin, pottery, and various art and crafts products flourished. At times the main business zone was near the old fort area (present Central Jail). Chawk Bazaar was the principal market then, known as Badshahi Bazaar.

For ministers and high officials, and the elite of the city there were two different and colourful residential-cum-shopping complexes (unlike anything we know now) at Bakshi Bazaar and Dewan Bazaar. There was a business centre at present Bangla Bazaar location, which was the main commercial zone before the Mughal period.

In 15-16th C. AD Murshid Kuli Khan became the Mughal Governor of Bengal and transferred its capital from Dhaka to Murshidabad (now India). As a result the importance of Dhaka declined a little bit.

In the latter half of the 19th C., Dhaka's major export items were cloth, indigo, betel nut, saffron flower, soap, animal hide, shell bracelets and jewellery. By 1930 Chawk Bazaar became a wholesale market from a retail centre. New retail areas came to be established along Nawabpur Road and Islampur Road. Bangla Bazaar also developed into a retail trading centre in the latter part of the British rule.

In 1947, Dhaka became the capital of East Pakistan which to some extent boosted its trade and commerce. At that time Imamganj, Chawk Bazaar, Mitford, Islampur, Patuatuli, Bangla Bazaar, Farashganj, Badamtali, Postagola areas developed as wholesale market areas with warehouse facilities. The retail areas were located at Islampur, Patuatuli and Bangla Bazaar, and from Sadarghat to Jinnah Avenue (present Bangabandhu Avenue) along Nawabpur Road.

New Market was constructed in the early 1950s, Baitul Mukarram and Stadium Shopping centres in the early 60s. The retail sale also took place along some portion of Mymensingh Road, Old Airport Road, Mirpur Road and some other main roads of the city.

In 1971, following the War of Liberation Dhaka became the capital of a new nation. Overnight Dhaka rocketed in importance and grew rapidly as a prominent centre of international and national activities including that of trade and commerce.

In 1993 Dhaka had 106 markets for grocery shops under the management of DCC. The rest of retail trade has evolved as ribbon development along the main roads forming arterial shopping centre.

Over the last decade the trend in shopping has changed dramatically. Multilevel shopping with luxurious facilities is becoming more popular in the city. As life was becoming fast, time and services became more valuable than money. This demand has been the driving force for the development of multi-storied shopping centres all over the city.

Vertical circulation
In a multi-storeyed shopping complex vertical circulation may be divided in two groups

a) Traditional-- Stair and ramp

b) Electromechanical--Lift and escalator

Nowadays the term 'stair', 'stairs', 'staircase' and 'stair way' all have the same meaning. According to Ralph Sinnott in 'Safety and Security in Building Design' 'stair' is the term preferred in conversation; 'stairway' seems to be preferred for technical use.

Lift (elevator) is a machine designed to transport persons or materials between two or more levels in a vertical or substantially vertical direction by means of a guided car or platform.

Escalator is also power driven but an inclined, continuously moving, stairway used for carrying passengers from one level to another.

Safety measures for stair
a. Directing user's attention: people should be warned about

i. The presence of a stairway

ii. Change of floor surface of stairway and its lobby

iii. An inclination in wall decoration along the inclination of the steps

iv. An extended hand rail of stairway

b. Focusing attention on, and defining, steps

i. Steps must be clear

ii. Shadow, lines parallel to the edge of the treads must be avoided

iii. Handrails should be provided to clarify the presence of the steps

iv. Steps with open riser may be harmful: glare, lack of attention toward steps, vertigo may occur in such type of staircase

c. Proportion of steps:

i. In about 1672 Francois Blondel, director, Royal Academy of Architecture in Paris devised the formula, twice the rise (r) plus the going (g) equals twenty four inches (2r+g=24"). Minimum going = 9.5"

ii. The requirement of building regulations of England and Wales are met if 2r+g lies between 550 and 700mm (21.5-27.5")

iii. In Britain, for residential buildings

*maximum pitch for stairways serving only one dwelling is 42 degrees

* maximum pitch for stairways serving two or more dwellings is 38 degrees

* consensus of opinion prefers 30 degree

d. Minimum headroom requirement is 2000mm in Britain and 2030mm in the USA

Code and legislation (Building Construction Rules 1996 and Bangladesh National Building Code 1993)

a. Pedestrian ramp

i. The minimum width of a ramp shall not be less than

*1.1m for occupancy of more than 50

* 0.9m for occupancy less than 50

ii. The slope of an exit ramp shall not exceed 1:8 but for slopes steeper than 1:10 the ramp shall be surfaced with approved non-slip material or finished such as to effectively prevent slipping.

iii. Guards or handrails shall be provided on both sides of a ramp having slope steeper than 1:15.

b. Stair

i. In a building the maximum distance of an emergency exit (stair) will not be more than 25m and it will be separated from stair lobby and lift lobby and will be connected with the ground floor. (Note: Elevator or escalator is not considered as an emergency exit)

ii. Minimum width of stair in Small Shops and Markets is 1.5m

iii. Minimum width of stair in Large Shops and Markets is 2.0m

iv. Combination of riser and the tread dimensions shall be such that the sum of the riser height and tread depth shall be between 400mm and 425mm with a minimum tread depth of 215mm and a maximum riser height of 215mm. The tread depth includes the nosing and any increase due to slant riser face. The variation between depth of adjacent tread and height of adjacent riser shall not exceed 5mm.The difference between the largest and smallest riser or between the largest and the smallest tread shall not exceed two percent of the respective average dimensions in any flight of stair

v. The number of steps in a single flight shall be limited to 15

vi. The minimum clear headroom between flights of stair shall be 2.15m.The clear headroom may be reduced to 2.03m for not more than three flights in any staircase

vii. The minimum clear height of any passage below landing providing access to non- habitable and service space shall be 2.03 m. The minimum clear height of all other passages and spaces below landing shall be 2.15m

viii. Handrail shall have a minimum height of 0.9m measured from the nose of stair to the top of the handrail. When children are likely to use the stair, the balustrade design shall incorporate

ix. Escape stairways should be completely enclosed with fire resisting construction, and doors should be self-closing and fire resisting, according to Nizamuddin Ahmed in 'Industrial Architecture for Developing Countries'.

x. Each stair and elevator shall be identified by an alphabet in Bangla and posted with a sign and securely placed preferably on the wall of stair side of the lift door from which egress is to be made. The letters shall be 75mm square and shall be posted on a contrasting background, e.g. black on a white background.

Escalator

i. Escalators shall be located in the main line of circulation and in such a way the most persons entering the building can see it. Care shall be taken to eliminate interference to traffic movement.

ii. Escalators shall be discharged into an open area with no turns or choice of direction necessary. Ample space for people must be provided at the entry and exit landing of an escalator, space between the newel and the nearest obstruction in front of the escalator shall be a minimum of 3m.

iii. If an unloading area is restricted, such restriction as doors or gates shall be interlocked with the escalator to insure that the restriction is removed before the escalator can be run.

iv. The escalator shall have provision to run in both upward and downward directions. However it shall not run in one direction for one trip and reversed for the next. Starting, stopping or reversal shall be controlled only by an attendant and with the assurance that no passenger riding at that time.

v. Minimum headroom above escalator (minimum vertical clearance between the line of step nosing and the lowest edge of ceiling opening) shall not be less than 2.3m.

vi. Near the place of escalator installation, one lift with wheel chair facility shall be installed to facilitate vertical movement of disabled persons.

Present status
A look at some shopping centres in the city shall enable a better understanding of the present situation.

In this study six major shopping centres of the present time were taken into consideration. They are:

1. Rapa Plaza at Dhanmondi

2.Rifles Square in Dhanmondi

3.Eastern Plaza at Hatirpul

4.Century Arcade at Maghbazar

5.IDB Bhaban at Agargaon

6.Basundhara City at Panthapath

Conclusion
a. In most of the surveyed shopping centres the stairs are not properly designed for escape during a fire

b. Stairs or even those earmarked as emergency stairs are not enclosed for fire protection in some of the shopping centres

c. In some cases the distance between the stairs is more than the recommended distance of 45m; legislation demands 25m.

d. In most cases no fire door is provided

e. In most cases no provision for vent flow in staircases to create positive pressure in the stairs to stop fire flow from outside

f. No fire hood for escalators

g. Signs and symbols are not used to give direction and location of the escapes

h. Slip-resistant tiles are not used in the corridors, lobby and staircases

Recommendations

There is wholesale negligence and ignorance in the design of vertical circulation in the shopping complexes in respect to fire, safety and security. If this be the situation in major designed complexes, the dangerous situation in the other shopping centres is not hard to imagine. In most cases no standard is followed in designing of the vertical circulation to protect against fire. Even the details are sometimes ignored, such as the direction of door swing, tread-riser ratio, finish material, and provision of single side railing.

As multi-storeyed shopping centres are becoming unavoidable and essential aspects of our city life, Architects and building owners should be more careful about the very vital vertical circulation. It may be pertinent to mention that the safety of a multi-storeyed shopping complex in a fire situation, that is Means of Escape, is primarily about its vertical circulation.

The author is a practising Architect and a postgraduate student at BUET