9.4.1 Drainage Equipment in Clean Operating Rooms

Type 525 Thermostatic Mixing Valve

  • Valve body: Bronze
  • Regulating piston and spring: Stainless steel
  • Temperature adjustment range: 36~53℃
  • Accuracy: ±2℃
  • Maximum pressure: 10kg
  • Maximum water temperature: 90℃
  • Caliber: $frac{1}{2}$~2in

Figure 9.3 Thermostatic Mixing Valve (Type 523)

Drainage equipment must be provided with a high water seal device below the drain outlet, and measures shall be taken to prevent the water seal from being destroyed.

[Reference] In clean operating rooms, in order to prevent contamination by foul air, all equipment in the room must be sealed to prevent communication with the outdoor atmosphere. The pipe below the drain outlet of washroom equipment leads directly to the outdoor sewer manhole; when there is no water, it communicates with the atmosphere and becomes a vent opening, through which foul gases from the sewer can sneak into the room and pollute the indoor air. To block harmful and toxic gases from entering the room through the drainage pipes, one method is to use drainage check valves; however, since the sewage carries a large amount of dirt, in which fibrous impurities easily become caught on components such as the check valve disc, the drainage check valve may fail to close tightly, impairing its gas-sealing function. Another method is to install a bent pipe section at the point where the sanitary fixture connects to the drainage piping system, with a certain amount of water retained in this section. When the sanitary equipment is in use, this bend can smoothly discharge the sewage while the gas is sealed off. This is the trap water seal below the equipment's drain outlet, which is currently the most effective method. The depth of this water seal must not be less than 50mm; this provision is determined based on factors such as pressure fluctuations within the drainage piping system and evaporation of the water seal. Any value smaller than this is considered unsafe.

The so-called high water seal is proposed in view of the previously low trap water seals, which were far less than 50mm, dried out easily, and allowed foul odors to escape. According to the industry standard for floor drain manufacturing, the minimum effective water seal storage of a DN50 floor drain should be greater than 165ml; that of a DN75 floor drain should be greater than 330ml; and that of a DN100 floor drain should be greater than 565ml. A certain volume and height of stored water is ensured so as to block foul sewer gases from sneaking into the room. Therefore, installing a high water seal device below the drain outlet of sanitary fixtures is of vital importance. To prevent the water seal from being destroyed, the following shall be done:

① When designing the drainage system, strictly comply with the Code for Design of Building Water Supply and Drainage. The drainage pipes shall have sufficient drainage capacity and shall be designed for gravity flow, with a pipe fullness ratio of 0.5; the purpose of installing various vent pipes is to balance the pressure within the pipes and protect the water seals of sanitary fixtures, so the vent system shall be arranged in accordance with Clauses 3.6.1 to 3.6.10 of the above code in the design; the lowest horizontal branch pipe connected to the stack shall maintain a certain distance from the bottom of the stack, otherwise the water seals of sanitary fixtures can easily be destroyed.

② Water-using equipment in hospital buildings must not use shared traps, and sanitary equipment in the surgical department is even more strictly prohibited from using shared traps; in this way, the water seal can be easily maintained. ③ Select a high-quality sealed floor drain, which has the function of opening during drainage and sealing when not draining; it can prevent the water seal from being lost and drying out, keep foul gases from entering the room, and also isolate the odor generated by the dirt accumulated in the floor drain.

9.4.2 Floor Drains

Floor drains are not allowed in clean operating rooms. Floor drains should be installed in scrub rooms and beside sanitary fixtures, and must be fitted with sealed covers.

As a sanitary fixture for draining surface water from the floor, the floor drain should be installed beside water-using equipment prone to splashing, as well as in places where the floor and walls need to be frequently washed with water. The floor drain should be installed level, secure, and leak-free. The top elevation of the floor drain should be 5～10mm below the nearby floor surface, and the floor should slope toward the floor drain at a gradient of $I=0.01$. In this way, surface water on the floor can be drained rapidly, and the water seal of the floor drain's trap can be regularly replenished with water, preventing the floor drain's water seal from being lost and drying out. However, floor drains—whether of the straight-through type, the type with a trap in the piping, or the sealed type with its own sealed cover—are all a critical gateway through which sewage flows into the sewer. Organic matter tends to deposit here and bacteria tend to breed; the decay and fermentation of organic matter readily generate harmful gases that seep into the room and pollute the indoor air. Therefore, floor drains should not be installed in operating rooms.

[Reference] With the development of medical technology, disinfection in operating rooms is carried out with chemicals rather than water, so floor drains are not needed in clean operating rooms. Floor drains installed in the surgical department must, first, have a sufficient water seal that meets the requirements of the Code for Design of Building Water Supply and Drainage, with the water seal of the floor drain not less than 50mm; second, have a simple structure with a smooth interior, unobstructed water flow, resistance to dirt accumulation, no overflow or gushing, good self-cleaning capability, and ease of cleaning; and third, be fitted with sealed covers to prevent water evaporation and the seepage of harmful gases from the sewer. Figure 9.4 shows the Huidong brand sealed clean floor drain (Model JDL-2-10), which is made entirely of stainless steel. An O-ring is provided under the sealed cover plate, and the stainless steel cover separates the room from the space inside the floor drain: first, to prevent the water in the water seal from evaporating and the water seal from being destroyed; second, to prevent foul gases from flowing back into the room.

9.4.3 Sanitary Equipment and Materials in the Clean Surgical Department

The clean surgical department should use sanitary fixtures, pipes, pipe supports, and fittings that do not easily accumulate dirt and are easy to clean.

[Reference] Sanitary fixtures within the clean surgical department should be made of white ceramic tiles or stainless steel, and should not be made of cement, terrazzo, or the like; generally, exposed traps should not be made of cast iron products with rough surfaces, but may be made of smooth-surface materials such as chrome plating and plastics; floor drains should not use cast iron grates, but should be made of smooth-surface materials such as rigid plastic, copper, and chrome-plated parts. For drainage pipes connected to equipment within the clean surgical department, if threaded connections are used, polytetrafluoroethylene (PTFE) tape should be used as the sealing material; lead oil, hemp fiber, and similar materials must not be used as sealing materials. The document issued by the Beijing Municipal Committee of Urban and Rural Construction and the Planning Committee (Jing Jian Cai [1998] No. 48) has stipulated that, starting from July 1, 1999, the use of ordinary cast iron bell-and-spigot drainage pipes is prohibited. Therefore, ordinary cast iron pipes are strictly forbidden, and their replacements are flexible cast iron pipes and machine-made cast iron drainage pipes. Flexible cast iron pipes and fittings are available in a complete range of specifications, with two connection methods: the coupling (clamp) type and the bell-and-spigot type; their advantages are long service life and convenient maintenance. Machine-made cast iron drainage pipes feature high strength, corrosion resistance, smooth interior and exterior surfaces, and convenient installation, and use stainless steel clamp-type rubber sleeve joints. Plastic building drainage pipes, such as UPVC pipes, PSP pipes, and UPC spiral silencing drainage pipes, have also been widely adopted because of their smooth pipe walls, low resistance, and good wear resistance. The water filling test results of the drainage pipes in the operating room and the water flow test results of the drainage system after completion must meet the design requirements and the construction acceptance specifications.

9.4.4 The Sewage Vent System of the Sanitary Fixtures and Devices in the Clean Surgical Department Should Be Independently Installed

The vent system serves two functions: first, to discharge the foul gases emitted from the indoor drainage system into the atmosphere; second, to supply air to the drainage stacks so that water flows smoothly, reducing the amplitude of pressure fluctuations in the drainage pipes and preventing the destruction of the water seals of sanitary fixtures. Therefore, buildings of more than one story should be provided with vent pipes for ventilation, and the vent pipes must lead directly to the outdoors and must not be connected to air ducts or smoke flues. Since the locations of the hospital buildings containing clean surgical departments vary, the sewage vent systems take different forms; the vent pipes may be of various types, such as stack vents extending through the roof, dedicated vent pipes, or loop vents. However, whichever type is used, in order to prevent foul gases from other sewage systems from entering the clean surgical department, the vent system should not be shared with other medical rooms. The sanitary fixtures and devices within the clean surgical department should also have their own independent vent piping.

9.4.5 The Horizontal Drainage Pipes in Clean Operating Rooms Should Be One Size Larger Than Conventional Ones

The diameters of the drainage pipes of the main structures in hospitals should be enlarged by one size compared with conventional practice, and anti-clogging, anti-leakage, and anti-corrosion measures should be taken measures. Hospitals have many types of pipelines with long runs, and when a fault occurs, walls have to be broken open, which is very inconvenient. Moreover, a relatively large amount of waste is generated during surgery. To prevent drainage pipes from becoming blocked, appropriately increasing the diameter of the drainage pipes in operating rooms can reduce the daily maintenance workload.

Figure 9.4　Clean floor drain (JDL-2-10 type)