Escape Route Capacity Calculation: Unit Width and Occupant Load (BYKHY Articles 32 and 33)

Short answer: the calculation has three steps. First, the occupant load of the floor is found with the factor from Annex 5/A of the Turkish Regulation on Fire Protection of Buildings (BYKHY); then the total exit width is calculated with the Article 33(1) formula; finally, the result is compared with the absolute minimum limits set by the Regulation. In medium-sized buildings it is often these minimum limits, not the formula, that govern the capacity.

Step 1: Occupant load

Under BYKHY Article 32(1), the occupant load factors given in Annex 5/A are used for the required escape and panic calculations. Article 4(bb) defines the occupant load factor as the usable area per person in a building, expressed in m²/person.

The note below Annex 5/A contains two rules. The occupant load is calculated on the net area for the uses in rows 1, 2, 3 and 4 of the table (halls, dance halls and bars, exhibition areas and studios, terminal waiting halls) and on the gross area for the others. In addition, in rooms where the number of people is known, the stated number of people is used, provided it is not less than the value calculated from the table: the number of fixed seats cannot go below the calculation, but it can go above it.

Article 31(6) allows a reduction: the floor areas of spaces such as toilets, changing rooms, stores and staff canteens, which serve other spaces but are not used at the same time as them, may be disregarded in the occupant load calculation. For mixed use, Article 31(5) requires either the use type with the strictest escape requirements to be taken as the basis or each part to be assessed separately.

The effect in building types where occupant load governs is shown in the articles on fire protection of shopping centres and fire protection of schools and dormitories.

Step 2: Unit width and the Article 33(1) formula

Under Article 32(2), the capacities of exit doors, escape stairs, corridors and other escape routes are calculated using a unit width of 50 cm. The number of people passing through the unit width is given by building use class in Annex 5/B. This detail is often confused: the factor is in Annex 5/A, and the number of people per unit width is in Annex 5/B.

Annex 5/B does not give this number as a single value; the exit door to the outside, other doors and corridor doors, escape stairs, and ramps and corridors are listed in separate columns. In the office buildings row these four values are 100, 80, 60 and 100 respectively. It is no coincidence that the stair column has the lowest number: movement on a stair is slow.

The Article 33(1) formula is as follows: the total exit width cannot be less than the value obtained by dividing the total number of occupants on a floor by the number of people per unit width and multiplying the result by 0.5 m.

Step 3: Minimum limits

The result of the formula is not sufficient on its own. Article 33(1) also sets minimum limits in the same paragraph:

• If the total number of occupants is between 50 and 500, the number of exits is determined so that the width of an escape route on the floor is not less than 100 cm
• Between 501 and 2000 occupants, it cannot be less than 150 cm
• For 2001 or more, it cannot be less than 200 cm
• If the escape route is also used, apart from this function, as a corridor and hall serving the spaces of the building, it cannot be less than 110 cm wide
• No exit, escape stair or other escape route may be narrower than the calculated values or than 80 cm

Article 33(2) adds that in high-rise buildings the width of escape routes and stairs cannot be less than 120 cm. Article 33(3) requires stairs wider than 200 cm to be divided by handrails into sections of not less than 100 cm and not more than 160 cm, and the corridor height to be not less than 210 cm.

Worked example: 1,200 m² office floor

The 1,200 m² floor area in the example is a chosen project input and does not come from the Regulation; 1.00 m and 0.60 m are results of the formula. All other numbers in the table are taken from Annex 5/A, Annex 5/B and the relevant article texts.

The result: the formula gives 60 cm for the corridor, but the value to apply is 110 cm. At this scale the minimum limits govern; the formula comes into play as the occupant load grows.

Travel distance is a separate calculation. Articles 32(3) and 32(4) state that the travel distance cannot exceed the values in Annex 5/B; the office buildings row of Annex 5/B gives 15 m in one direction without sprinklers and 30 m with sprinklers, and 45 m and 75 m respectively in two directions. Under Article 32(5), on a large floor subdivided into rooms, corridors and similar sub-divisions, the direct (straight-line) travel distance is accepted if it does not exceed 2/3 of the maximum distance permitted in Annex 5/B. Article 32(6) states where the measurement starts: the farthest point is taken 40 cm in front of the walls enclosing the space. The reasoning is covered in the article on the 40 cm travel distance rule.

Number and layout of exits

Article 39(1) requires at least 2 exits in all buildings unless otherwise stated, and requires the exits to be protected. Article 39(2) links the number to the occupant load: in high hazard spaces where 25 people is exceeded and in every space where 50 people is exceeded, at least 2 exits are mandatory; above 500, at least 3; above 1000, at least 4 exits.

The layout matters as much as the number. Under Article 39(3), where 2 exits are required in undivided single spaces, the distance between the exits cannot be less than 1/2 of the diagonal distance without a sprinkler system, or 1/3 with one. Article 39(4) applies the same logic to corridor layouts: in building use classes where exit distances are measured from the door, the distance between 2 escape stairs within a corridor cannot be less than half the corridor length without sprinklers, or 1/3 with sprinklers. Article 40(1) sums up the principle: escape routes and stairs are positioned as alternatives to each other and cannot be placed side by side.

There is an exception at small scale: under Article 32(8), in shops and similar premises on the ground floor, if the number of people is below 50 and the travel distance from the farthest point to the door opening to the outside is less than 25 m, a single exit to the outside of the building is accepted as sufficient.

Bottleneck check: where the width is measured

Article 33(5) states that widths are measured as clear widths. On escape stairs, only 80 mm of the projection formed by the handrail is included in the clear width. For a single-leaf exit door, the clear width is the dimension between the frame or rebate projection and the face of the leaf opened to 90 degrees, and it cannot be less than 80 cm or more than 120 cm; for a double-leaf door, the dimension is taken between the leaf faces with both leaves open at 90 degrees.

On site, every point that narrows the chain has a corresponding article.

1. Clear door opening width. What counts is not the leaf width but the dimension between the leaf open at 90 degrees and the frame (Article 33(5), Article 47(4)).
2. Stair handrail. Only 80 mm of the projection counts towards the clear width (Article 33(5)).
3. Door leaf opening onto the landing. It cannot be positioned so as to narrow the escape route by more than 1/3 (Article 41(5)).
4. Corridor height. It cannot be less than 210 cm (Article 33(3)).
5. Permanent narrowing and visibility in the corridor. Article 30(4) requires escape routes to be kept freely accessible and unobstructed, and Article 33(6) requires exits to be clearly visible and kept free of obstructions.

The compartment layout and the exit layout are set up together; the articles on fire compartment areas and escape routes and stairs complete these two sides.

Field note

In an educational building the occupant load had been calculated correctly and the widths provided. On a visit a year later, rows of cupboards had been placed along one side of the corridor; the usable width had dropped below the 110 cm minimum that Article 33(1) sets for corridors. Article 30(4) requires escape routes to be kept unobstructed; this was an operational, not a design, violation.

A second example: a production facility had two escape doors, but both were on the same facade with only a few metres between them. Article 39(3) states that in undivided single spaces the distance between two exits cannot be less than 1/2 of the diagonal without sprinklers. The calculation had been made on the basis of two exits, but the layout did not satisfy this paragraph.

The lesson: a capacity calculation is not arithmetic but a layout decision. After finishing the calculation, ask two questions on the plan: does the distance between the exits satisfy Articles 39(3) and 39(4), and will the calculated width still be there six months from now?

Checklist

• ☐ The Annex 5/A factor and the net/gross area distinction applied correctly for each space
• ☐ The number of people per unit width taken from Annex 5/B, separately for doors and stairs
• ☐ Total exit width calculated with the Article 33(1) formula
• ☐ Result compared with the 100, 150, 200 cm, 110 cm and 80 cm minimum limits
• ☐ Number of exits determined from the Article 39(2) thresholds
• ☐ Distance between exits checked against the 1/2 or 1/3 of the diagonal rule (Article 39(3))
• ☐ Travel distances read from Annex 5/B, measurement starting 40 cm in front of the wall (Article 32(6))
• ☐ Clear door width measured between the leaf open at 90 degrees and the frame (Article 33(5))
• ☐ Absence of permanent narrowing in the corridor confirmed and notified to the operator in writing

FAQ

How is the occupant load calculated?

Under BYKHY Article 32(1), the occupant load factors in Annex 5/A are used for the required escape and panic calculations. Annex 5/A gives the factor in m² per person; for example 10 m²/person for offices and 30 m²/person for stores and car parks. According to the Annex 5/A note, the net area is used for the uses in the first four rows and the gross area for the others, and in rooms with a known number of people that stated number is used, provided it is not less than the calculated value.

What does the 50 cm unit width mean?

Under BYKHY Article 32(2), for exit width, the capacities of exit doors, escape stairs, corridors and other escape routes are calculated using a unit width of 50 cm. The number of people passing through the unit width is given by building use class in Annex 5/B; this number differs for doors, stairs and corridors.

What is the formula for total exit width?

Under BYKHY Article 33(1), the total exit width cannot be less than the value obtained by dividing the total number of occupants on a floor by the number of people per unit width and multiplying the result by 0.5 m. In addition, the number of exits is determined so that an escape route on the floor is not narrower than 100 cm if the total number of occupants is between 50 and 500, 150 cm between 501 and 2000, and 200 cm for 2001 or more.

How many exits does a floor need?

BYKHY Article 39(1) requires at least 2 exits in all buildings unless otherwise stated. Under Article 39(2), at least 2 exits are mandatory in high hazard spaces where 25 people is exceeded and in every space where 50 people is exceeded; at least 3 exits if the number of people exceeds 500, and at least 4 exits if it exceeds 1000.

References

1. Turkish Regulation on Fire Protection of Buildings (BYKHY), Official Gazette 19.12.2007/26735 and amendments; Articles 4(aa), 4(bb), 30(4), 31(5), 31(6), 32(1)-32(6), 32(8), 33(1)-33(6), 39(1)-39(4), 40(1), 41(5), 47(4), Annex 5/A, Annex 5/B. mevzuat.gov.tr (consolidated text)

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