Interior building decoration design is part of architectural design. The materials used for decoration are all relatively fire-sensitive materials, and the vast majority of building fires begin to spread and expand from indoors. Therefore, the combustion performance of interior decoration materials is a factor affecting fire conditions …one of the important factors affecting fire development and personnel safety. The main influences of decoration materials on fire and personnel safety include the following aspects: affecting the rate of fire growth from ignition to flashover, increasing the fire load density, producing toxic smoke, and reducing indoor visibility. Therefore, the interior decoration design of a building must take into account the building's fire protection needs.

[Reference] Fire load density is the ratio of the total heat of combustion generated by the complete burning of all combustible materials in a building interior to the reference area of that interior. In engineering practice, the floor area is generally taken as the reference area.

10.2.1 General Principles of Design

The interior decoration of a hospital clean operating department mainly comprises the walls, ceiling and floor, as well as indoor furniture and ornaments. In the design, full consideration should be given to the airtight characteristics and functional requirements of the space within the clean operating department, the conflicts among decorative effect, safety in use, and disinfection and cleaning should be properly handled, non-combustible and flame-retardant materials should be adopted as far as possible, and materials that produce large amounts of smoke or toxic gases when exposed to high temperature or during combustion should be avoided. In accordance with the patterns of high-temperature smoke flow and fire development after a fire breaks out inside a building, Chinese codes require that materials be selected such that, within a room, the combustion performance of the decoration materials decreases progressively from the ceiling to the floor.

(1) For clean areas, if the windows cannot be opened or are usually kept in a closed state, their interior decoration design should be treated as that for windowless rooms.

(2) The ceilings, walls and floors of staircases without natural lighting, enclosed staircases and smoke-proof staircases should all use Class A decoration materials.

(3) For the horizontal evacuation corridors of a building and the lobbies of safety exits, the ceiling decoration materials should be Class A decoration materials, and other parts should use decoration materials of a grade not lower than Class B₁.

(4) The combustion performance grades of decoration materials for various parts of civil buildings should not be lower than the requirements in Table 10.1.

Table 10.1 Combustion performance grades of decoration materials for various parts of civil buildings

Building Building scale and nature Ceiling Wall Floor Partition Fixed furniture Decorative fabric Curtains Decorative fabric Drapes Decorative fabric Furniture upholstery Other decoration materials
Single-story and multi-story hospital ward buildings With clean operating rooms A B₁ B₁ B₁ B₂ B₁ — — B₂
Single-story and multi-story office buildings and multi-purpose buildings Office buildings and multi-purpose buildings with central air-conditioning systems A B₁ B₁ B₁ B₂ B₂ — — B₂
Single-story and multi-story office buildings and multi-purpose buildings Other office buildings and multi-purpose buildings B₁ B₁ B₂ B₂ B₂ — — — —
High-rise multi-purpose buildings and hospital ward buildings Class I buildings A B₁ B₁ B₁ B₂ B₁ B₁ B₂ B₁
High-rise multi-purpose buildings and hospital ward buildings Class II buildings B₁ A B₂ B₂ B₂ B₂ B₂ B₂ B₂
High-rise office buildings and scientific research buildings Class I buildings A B₁ B₁ B₁ B₂ B₁ B₁ B₁ B₁
High-rise office buildings and scientific research buildings Class II buildings B₁ B₁ B₂ B₁ B₂ B₁ B₂ B₂ B₂

(5) Decoration should not block fire protection facilities (such as fire hydrants, automatic alarm devices, automatic fire extinguishing facilities, smoke control and exhaust facilities, etc.) or evacuation indication signs and exits, nor should it change the opening direction of evacuation exit or safety exit doors, reduce the effective evacuation width of evacuation exits, safety exits and evacuation routes, or hinder the normal use of these facilities. The so-called effective evacuation width refers to the minimum clear width necessary for the safe evacuation of occupants, calculated according to the number of people to be evacuated specified by the code and the evacuation index per hundred persons. According to common international practice, this width should generally also take into account the boundary effect of the exit or evacuation route. When considering the width of evacuation routes within a fire compartment, the effective width of the evacuation route or evacuation exit should be calculated, rather than its clear width, and attention should be paid to this point.

Other fire protection design of the interior decoration of buildings should comply with the relevant provisions of the national standard Code for Fire Prevention in Design of Interior Decoration of Buildings (GB50222-95). 【Reference】　Effective evacuation width. When walking, people swing their arms on both sides to maintain body balance; therefore, when evacuating along a passage, evacuees keep a certain distance from the side walls instead of walking right up against the side walls or handrails. As a result, a boundary layer exists at the boundary of an evacuation passage or evacuation exit, and this portion of the width cannot be utilized by evacuating occupants. Therefore, when performing evacuation calculations, the width of the boundary layer should be deducted, and the width should be taken as the clear width of the evacuation passage or exit minus the boundary layer width. Table 10.2 gives the boundary layer width values present in various types of passages.

Table 10.2　Boundary layer width values in various types of passages

Type of evacuation passage Stairs Guardrails, handrails Seats in theaters, benches in gymnasiums Corridors, ramp walls Obstacles Spacious halls, walkways Doors, archways
Boundary layer thickness/cm 15 9 0 20 10 46 15

10.2.2　Classification and Grading of Decoration Materials

(1) Classification and grading.

The decoration materials in the clean operating department of a hospital can, according to their location of use and function, be classified into ceiling decoration materials, wall decoration materials, floor decoration materials, partition decoration materials, fixed furniture, decorative fabrics (such as curtains, drapes, bedspreads, furniture upholstery, etc.), and other decoration materials (such as stair handrails, picture rails, skirting boards, curtain boxes, and radiator covers, etc.).

The burning performance of decoration materials is classified, with reference to the national standard Classification Method for Burning Behavior of Building Materials (GB8624), into four grades: non-combustible materials (i.e., Grade A), flame-retardant materials (i.e., Grade B₁), combustible materials (i.e., Grade B₂), and flammable materials (i.e., Grade B₃). Most materials are graded in accordance with the Classification Method for Burning Behavior of Building Materials (GB8624); however, floor decoration materials are graded according to the Determination of Critical Radiant Flux of Floor Coverings—Radiant Heat Source Method (GB11785); decorative fabrics are graded according to the Determination of Flame Retardancy of Textile Fabrics—Vertical Method (GB5455); and plastic materials are graded according to the Oxygen Index Method (GB2406), the Horizontal Burning Method (GB2408), and the Vertical Burning Method (GB4609). In the national standard Code for Fire Prevention in Design of Interior Decoration of Buildings (GB50222), the latter three types of decoration materials are graded as Grade B₁ and Grade B₂ respectively.

【Reference】　Building decoration materials.

① According to China's current fire test methods and grading methods for building materials, paper-faced gypsum board has a burning performance of Grade B₁; however, when paper-faced gypsum board is installed on steel keels, it may be used as a Grade A decoration material.

② When the surface of plywood is coated with first-grade finishing fire-retardant coating, it may be used as a Grade B₁ decoration material. When used for wall decoration, the fire-retardant coating may be applied on the side facing the interior of the room; when used for suspended ceiling decoration, the fire-retardant coating should be applied on both sides.

③ Paper or fabric wallpaper with a unit weight of less than 300g/m² may be used as a Grade B₁ decoration material when directly pasted onto a substrate with a burning performance of Grade A.

④ Inorganic decoration materials applied onto substrates with a burning performance of Grade A may be used as Grade A decoration materials; organic decorative coatings applied onto Grade A substrates with a wet coating ratio of less than 1.5kg/m² may be used as Grade B₁ decoration materials.

⑤ When different decoration materials are used for layered decoration, the burning performance grades of the decoration materials in all layers should comply with the requirements of the Code for Fire Prevention in Design of Interior Decoration of Buildings. Composite decoration materials should be tested as a whole by a professional quality supervision and inspection institution, and their burning performance grades should be determined.

⑥ When porous or foam plastics are locally used on the surfaces of ceilings or walls, their thickness should not exceed 15mm, and their area should not exceed 10% of the ceiling or wall area of the room.

(2) Polystyrene in composite panels and its combustion toxicity.

When the combustible substances produced by the thermal decomposition of high polymers are mixed with air in a certain proportion and reach the flash temperature (also called the flash point), the ignition temperature (also called the fire point), or the spontaneous ignition temperature (also called the autoignition point), combustion begins. Generally, the fire point is 20～30℃ higher than the flash point. The flash point of polystyrene is 360℃, its fire point is about 380℃, and its autoignition point is 495℃. The structure of polystyrene composite panels The form determines that polystyrene does not come into direct contact with open flame during fire exposure; it undergoes deformation, gasification, and flameless combustion as a result of heat conducted through the cement mortar protective layer.

Polystyrene thermal insulation board: Polystyrene core boards are hardly ever used in external building envelope systems, but are commonly used for internal thermal insulation in buildings (such as food processing plants). The fire behavior of polystyrene differs from that of rigid polyurethane (PIR/PUR); it is a thermoplastic material that readily melts, shrinks, and burns, with a softening temperature of approximately 100℃ and a melting temperature of approximately 180℃. As the temperature rises, polystyrene melts, and the heated surface shrinks to form cavities, allowing flames to enter the cavities, thereby producing molten drips that flow out from both the inner and outer sides of the envelope surface. Tests have shown that once flames enter the board core, fire can spread without restriction between the facings, burning and damaging the core material. If the facings are not securely installed, premature collapse will occur, severely affecting the rate of flame spread. As long as the facings and all joints are reliably installed, sudden flame spread onto the wall will not occur.

The main manifestations of polystyrene thermal insulation boards in large-scale fire tests are: melting and shrinking, production of molten drips, intensification of the fire, hidden flame spread within the facings, and collapse of frameworks that insecurely hold the facings.

Combustion toxicity refers to the toxic gases derived from combustible materials during combustion or thermal decomposition. When people in the fire-affected space inhale such gases, they die from their toxic effects. In view of the harm combustion toxicity causes to the human body, many countries have carried out extensive research on fire toxicity. Test results show that the gaseous products produced when common organic polymers burn in air include carbon monoxide (CO), carbon dioxide (CO₂), sulfur dioxide (SO₂), ammonia (NH₃), methane (CH₄), hydrogen cyanide (HCN), hydrogen chloride (HCL), and so on. Among these, CO, CO₂, and HCN are the most important combustion toxic gases that cause death in fires.

Polystyrene foam generates some toxic gases when it burns. Tests show that when polystyrene burns, it produces carbon monoxide, carbon dioxide, methane, ethylene, and ethane, but does not produce hydrogen cyanide. The content of methane, ethylene, and ethane accounts for only about 2% of the total gas content. The Lindberg horizontal tube furnace developed by the National Aeronautics and Space Administration (NASA) is dedicated to toxicity testing. In the test, 4 white mice are placed in the furnace and exposed to the combustion environment for 30min, with mortality and incapacitation measured every 10min. Based on actual measurements, test results for 27 organic materials were obtained, as detailed in Table 10.3. In terms of combustion toxicity, the toxic gas doses of flaming combustion and flameless combustion are different. The toxicity produced by the flaming combustion of polystyrene is greater than that produced by flameless combustion, with the ratio between the two being approximately 1.76. Generally, the combustion of polystyrene in sandwich panels is essentially flameless combustion.

Table 10.3　Relative Toxicity of Polymer Materials Determined with the Lindberg Horizontal Tube Furnace

Item Time to death/min Time to incapacitation/min Number of animals
Acrylic/rayon (7/3) 4.54±1.0 3.74±0.23 8
Wool 7.60±2.90 5.45±1.77 16
Silk 8.94±0.01 5.84±0.12 8
Leather 10.22±1.72 8.16±0.69 8
Red oak 11.50±0.71 9.09±1.00 8
Polypropylene 12.98±0.52 10.75±0.18 8
Polyester (fabric) 13.30±1.95 8.85±3.25 8
Aromatic polyamide 13.50±0.98 11.79±1.71 8
Polyurethane (rigid foam) 14.05±0.60 12
ABS 14.48±1.59 10.58±1.32 8
Douglas fir 14.76±0.90 11.79±0.90 12
Cotton 15.10±3.03 9.18±3.61 8
PMMA 15.58±0.23 12.61±0.06 8
Polysulfone 15.72±1.40 10.61±1.33 8
Butyl rubber 15.58±0.97 9.50±0.61 12
Polyvinylidene chloride 15.86±2.74 6.50±0.11 8

Table 10.3 (continued)

Item Time to death/min Time to incapacitation/min Number of animals
Nylon-6.6 16.34±0.85 14.01±0.13 8
Polyurethane (soft foam) 16.60±1.14 10.21±0.86 8
PVC 16.84±0.93 12.67±2.84 8
Phenolic resin 18.81±4.84 12.92±3.22 16
Polyethylene 19.84±0.29 8.36±0.80 8
Poly(ethylene) 20.50±2.05 16.94±2.39 8
Natural rubber 22.13±1.73 15.35±4.32 12
Bisphenol A polycarbonate 23.04±5.25 16.02±1.85 8
SBR 24.11±2.08 15.73±6.25 12
Polystyrene 26.16±0.12 19.04±0.39 8
Chlorinated polyvinyl chloride 27.35±4.21 11.11±6.21 8

(3) Domestic standards and methods for combustion tests of rigid foam plastics.

At present, China has mainly three national codes or standards directly related to combustion test methods in the application of rigid foam plastics, namely the Code for Fire Protection Design of Buildings (GBJ-16-87), Rigid Polyurethane Foam Plastics for Thermal Insulation of Buildings (GB10800-89), and the Classification Method for Burning Behavior of Building Materials (GB8624-97). To implement these standards, approximately ten related national-level test methods have been formulated successively.

The newly revised Classification Method for Burning Behavior of Building Materials (GB8624-97) added the oxygen index indicator for a variety of materials. However, due to the limitations of this indicator, it is hardly used internationally as a test indicator required by standards. Domestic researchers once used three methods, namely the oxygen index method (the minimum oxygen concentration required for a material to sustain combustion), the ISO ignitability (thermal radiation) test, and the hydrogen-oxygen flame ignition (convection) method, to evaluate the burning performance of 10 commonly used building materials, with the results shown in Table 10.4. The results show that the flame retardancy of these materials appears disordered in the ranking of test results obtained by these test methods. Taking flame-retardant polyurethane as an example, measured by the oxygen index (24.5), it ranks second among these 10 materials. However, in the ISO ignitability test and the hydrogen-oxygen flame ignition method test, its flame retardancy is the worst. Obviously, using the level of the oxygen index to measure the ease of combustion of materials is unreliable. Therefore, caution should be exercised when selecting the oxygen index method as a regulatory evaluation method for the burning performance of building materials. Of course, as a method for evaluating the burning performance of materials, the oxygen index method, since it can give relatively accurate figures, is widely used to evaluate the flame retardancy of materials in laboratories and in the selection of product formulations.

Table 10.4 Comparison of the Oxygen Index Method, the ISO Ignitability Test, and the Hydrogen-Oxygen Flame Ignition Test

Material Oxygen index method ISO ignitability test Hydrogen-oxygen flame ignition method
Flame-retardant polyurethane foam 8 10 5
Polystyrene board 1 9 4
Glass fiber and nylon reinforced polyester board 6 8 6
High-density polystyrene 3 7 3
PMMA board 2 6 7
Laminated fiberboard 4 5 8
PP board 7 4 9
PVC board 9 3 2
PE board 10 2 10
Low-density PE board 5 1 1

Note: The tests were completed at the Fire Research Laboratory of the National Research Council of Canada. (4) Rigid polyurethane is a thermosetting material that hardens and chars when exposed to fire, whereas polystyrene is a thermoplastic material that melts and can be ignited when exposed to fire. Tests on rigid polyurethane boards showed that, for both PUR and fire-resistant PIR insulation materials, there was no concealed flame spread between the decorative facings. The inner decorative facing warped slightly and the joints remained intact; at locations immediately adjacent to the fire source, flames did indeed enter the board core through the joints, but inspection revealed only localized charring. For rigid polyurethane boards, the heat of the fire causes the insulation material to decompose gradually and form a stable, protective char. Initially, only the insulation material in contact with the inner decorative facing chars, thereby protecting the insulation board. As the fire develops, the char layer gradually thickens until the fire is extinguished or dies out. During this process the board emits smoke. However, fire-resistant polyurethane (PIR) produces little smoke, whereas other rigid polyurethane (PUR) produces a relatively large amount of smoke.

The main fire characteristics of rigid insulation boards in large-scale fire tests are: the structure remains intact; no flame spread within the board core; compliance with thermal insulation standards; no flaming molten drips; gradual decomposition above 300℃ with relatively small smoke production; loss of adhesion between the facing panel and the core material near the heat source without endangering the overall integrity; no additional hazard to firefighters.

Tests on rigid polyurethane boards with sprinkler heads installed: the rigid polyurethane board tests were repeated with the addition of sprinkler heads to examine their effect on the boards. In accordance with the installation spacing, two sprinkler heads were installed near a wall constructed of combustible materials. The tests were activated manually to ensure that the fire was fully developed before activation. The results were: within 30s, the burning flames at the side wall joints were extinguished, the color of the smoke turned gray, and then gradually turned white as the test proceeded. The sprinkler arrangement could only wet the first layer and the rear side of the side wall (wood crib), so the temperature at these locations dropped from 550℃ to 100℃ within 1min of sprinkler activation, and the average temperature of the smoke layer dropped to 270℃.

The use of a water sprinkler system can not only control a fire in the traditional sense, but also, in fires where rigid polyurethane boards are present, keep the temperature at the fire scene below the level at which the board core material would burn.

The main fire characteristics of rigid polyurethane boards in large-scale fire tests (with water sprinkler systems installed) are: limiting combustion and the involvement of the boards in the fire; limiting the damaged area of the boards; reducing smoke production.

(5) Rock wool thermal insulation boards or high-density rock wool thermal insulation boards.

These boards have a normal density of 100kg/m³ and are mainly used as exterior envelope structures where the building code requires a fire resistance rating greater than 30min (insulation), or in other locations with high fire hazard.

The performance test results of high-density rock wool boards are as good as those of fire-protection products. Like all thermal insulation materials, and like all thermal insulation systems, these boards can also be destroyed by warping of the inner facing when exposed to fire, and the board core needs to be replaced due to the effects of temperature.

The main fire characteristics of rock wool thermal insulation boards in large-scale fire tests are: maintaining structural stability; no flame spread within the board core; minimal effect of the board core material on the fire; maintaining the integrity of the insulation material; adhesives and resins affected above 300℃; loss of adhesion near the heat source, with damage to the boards (warping).

(6) Glass fiber and rock wool boards.

Comparative tests were conducted on a standard multi-component assembly system consisting of a lining board, 86mm thick insulation wool, and an external protective board, and the combustion performance of glass fiber (11kg/m³) and rock wool (23kg/m³) was evaluated.

Mineral fibers themselves are non-combustible materials and will not aggravate the fire. However, the binders connecting the fibers and the breathable membranes can burn and have a limited effect on the fire and on the amount of smoke produced. Tests showed that this low-density fiber wool undergoes severe shrinkage at temperatures above 600℃. For glass wool, at 850℃ the glass shrinks to a thickness of only 10mm. Higher-density rock wool also exhibits severe damage near the fire source, but the shrinkage is smaller and the reduction in thermal insulation performance is also smaller.

The main fire characteristics of site-assembled systems of glass fiber and rock wool thermal insulation boards in large-scale fire tests are: maintaining structural stability; shrinkage of the insulation material at temperatures above 500℃; loss of thermal insulation performance at temperatures above 850℃; minimal effect of the board core material on the fire; loss of adhesion near the heat source, with damage to the boards (warping). (7) The basic conditions for the construction and design of clean operating rooms derive precisely from the particularity of their functions: ① the requirement to maintain a near-sterile clean environment to the greatest extent possible; ② the requirement to create the most comfortable environment conducive to work for medical staff. Therefore, the walls are generally required to be pollution-free, highly clean walls. Such walls should preferably use panels with properties such as low static electricity that reduces dust adhesion, non-combustibility, comfortable matte colors, rot resistance, easy maintenance, non-toxicity, impact resistance, and waterproofing. Figure 10.1 shows a photograph of actual operating room wall panels made of such fireproof boards.

Figure 10.1　Operating room with fireproof board wall panels