The History of Furniture Construction

Anthropometric Measures of the Human

Anthropometry (Gr. anthropos—human, metreo—measure), according to the def­inition in the encyclopaedia PWN, is a group of technologies of making mea­surements of the body or skeleton of a modern and fossil human being, and it enables an accurate and comparable study of diversity and variability of measured characteristics of the human in his personal and evolutionary development.

Knowledge of the human’s dimensions, called anthropometric dimensions, constitutes the basic component of the knowledge base necessary to shape work­stations in terms of the user’s comfort and functionality of the designed products. The application of these dimensions enables one to carefully design a usable space, choose the appropriate size of furniture and their component parts and propose the most favourable arrangement of this furniture in relation of each other and the user.

The frequency distribution of anthropometric characteristics generally takes the form of a Gaussian distribution. Therefore, when there is no possibility of designing furniture for 100 % of the population, in literature, it is recommended to adopt border values of characteristics corresponding to the lower centile (5C), upper centile (95C) and average value (50C). The threshold values determine what number of a given population is located in a given range. Hence, the lowest dimension defined by centile 5C is not achieved by only 5 % of the population, while 95 % of the population is found below centile 95C. Centile 50C (average)

symmetrically divides the population of users into ones achieving a specific dimension and those who do not achieve this dimension (Batogowska and Malinowski 1997). According to the principle of restrictive measures, a properly designed piece of furniture should, therefore, take into account the dimensions adjusted to the dimensions of the users, at least 90 % of the population, that is those, whose dimensions fall between the values of the 5th and 95th centile (Fig. 3.16). Thus, the percentage of people, for whom a usable space or piece of furniture will not be adjusted, will amount to 5 and 10 %, respectively.

Usually, it is assumed that the dimensions that correspond to the characteristics

• of the 5th centile are applied to determine dimensions, borders of zones of reach, positions of important handles, fittings and locks,

• of the 95th centile are used for internal dimensions, spaces for the lower limbs, trunk, etc.

For these reasons, furniture for lying down should be designed for users from the population represented by the 95th centile and furniture for work and dining according to the characteristics of values of the 50th centile, as well as furniture for storage according to 5th or 50th centile. In order to unify the application of this rule, anthropometric data are provided in the system (for men and women) of the 5th, 50th and 95th centile. Figure 3.17 and Table 3.2 summarise the basic anthropo­metric features for a person in a seated position, and Fig. 3.18 and Table 3.3 illustrate the anthropometric features for a person in a standing position.

In the practice of design, there is a fundamental difficulty, due to the variation in the dimensions of individual members of the population. The reason for this dif­ferentiation is ethnic origin, gender, height, development, age and social and pro­fessional class. In order to facilitate the selection of these dimensions, anthropometric data have been provided below for the adults of selected countries

of the European Union for the purpose of designing (Jarosz 2003) (Tables 3.4, 3.5, 3.6, 3.7, 3.8 and 3.9).

Often, designs include the individual character of the workstation and place for sleep or rest. Then, the designer should both independently calculate the value of individual measures and specify the value of the centile representing the user, for whom the project is created (Dirken 2001; Haak and Leever-van der Burgh 1994; Molenbroek 1994; Panero and Zelnik 1979; Pheasant 2001). The method of cal­culating the dimension for centile C has been given below:

SC = SR ± Z • SD (3.8)

where

• SC—dimension calculated for centile C,

• SR—average measures established on the basis of anthropometric tables of a selected population,

• Z—coefficient established from Table 3.10. The coefficient can assume ± values. For dimensions above the average, the coefficient has the value (+), while for dimensions below the average value, the coefficient has the value (—),

• SD—standard deviation for the dimension SR determined on the basis of anthropometric tables of the selected population.

Example

If the average height of an adult male amounts to SR = 1766 mm, the standard deviation of this measure amounts to SD = 76 mm, and then, in reading the value of coefficient Z (for the corresponding centile) from Table 3.10, we calculate the sought height value:

When designing interiors, we refer the dimensions of many objects to the dimension of the dominating object or also the dominating dimension of the user. By knowing his main features, determining the functionality of the designed fur­niture piece or interior, as well as the average value and standard deviation of this dimension, the value of coefficient Z can be calculated, which will allow to design other dimensions of a given product or other objects:

Z =(SC-SR)/SD. (3.9)

Examples

A man who is 1920 mm tall represents the group of tall people, and 98.87 % of the population is shorter, because

Z = (1920-1706)/94 = +2.28,

and in Table 3.10, the coefficient Z = + 2.28 corresponds to the 98.87th centile.

In a kitchen furnished with cabinets with a height of 900 mm, the lowest usable plane is the bottom surface of the sink away from the floor by 750 mm. The centile corresponding to the first height specifies how many users will be taller:

Z = (750-766)/43 = -0.37.

Based on the calculated Z value, it can be concluded that 100 % - 35.57 % = 64.43 % of tall users will have to bend down while doing the dishes and straighten up again when moving on to work at the cabinets.

When designing, the dimension differences resulting from the age of users using the same furniture should also be taken into account. Compiling the average dimension for a man and woman of different ages can be conducted on the basis of the equation:

SRa+b = %A • SRa + %B • SRb (3.10)

and

SDA+b = %A • SDA + %B • SDB + %A • %B • (SRa - SR#)2 (3.11)

When compiling the dimensions for any two groups, one needs to know the average dimensions and standard deviations of these dimensions for each of the groups. For example, at the age of 65, women dominate (58.65 %), while for the average population, the representation of gender is more uniform (A = 50.27 % of men and B = 49.73 % of women). Assuming the average height of the body of a man aged 18-65 years old equal to, e. g., SRA = 1766 mm and standard deviation SRA = 75.46 mm, as well as the dimensions of women corresponding to these parameters: SRB = 1646 mm and SRB = 67.91 mm, the average height of the human body between the ages of 18 to 65 years old should amount to:

SRa+b = 0.5027 • 1766 + 0.4973 • 1646 = 1706.32 mm,

SDa+B2 = 0.5027 • 75.45962 + 0.4973 • 67.91132 + 0.5027 • 0.4973 • (1766-1646)2, SDa+B2 = 2862.45 + 2293.52 + 3599.90 = 8775.87,

SDa+b = 93.6 mm.

Adding and subtracting dimensions takes place according to the superposition principle:

SRa ± B = SRa ± SRb, (3.12)

SDA±b = SDA + SDB±2 • r • SDa • SDb. (3.13)

Coefficient r (Table 3.11) expresses relations between two dimensions of the body.

Example

In order to determine the height of the worktop of a table, the seat height should be set at SRa = 446 mm and height from the seat to the surface of the worktop SRB = 244 mm. For the adult population of users, the result of this compilation provides the average value:

SRa+b = 446 + 244 = 690 mm,

SD2 = 262 + 242 + 2 • 0.65 • 26 • 24 = 2063.2,

SD = 45.42 mm.

The average height between the floor and the worktop surface should therefore amount to 690 mm. In order to calculate the height taking into account the base under the feet (also the soles of footwear), an additional 30 mm should be con­sidered. The new height of the worktop should therefore amount to 720 mm. Of course, a height that takes into account the needs of the population from 1 to 99 % would be satisfying, and therefore

1C = SR—2.33 • SD = 690-2.33 • 45.42 = 584 mm + 30 (sole) = 610 mm, 99C = SR + 2.33 • SD = 690 + 2.33 • 45.42 = 789 mm + 30 (sole) = 820 mm.

In the group of office furniture, chairs are often equipped with a lifting and tilting mechanism of the seat. Therefore, the height of the worktop should be 60 mm higher than at traditional chairs. According to the calculated values, the height of the worktop should range from 610 to 880 mm.