Maintenance and repair of insulation for chemical processing equipment and pipelines
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Maintenance and Repair of Insulation for Chemical Processing Equipment and Pipelines I. General Provisions 1. Scope of Application These regulations apply to the maintenance and repair of insulation on equipment and pipelines in chemical processing enterprises. 2. Structural Composition 2.1 Insulation of Equipment and Pipelines Its structure includes insulation structures and cooling insulation structures. 2.2 An insulation structure generally consists of an insulating layer (thermal insulation layer) and a protective layer. Insulation structures located in outdoor, underground, or humid conditions should be equipped with a moisture barrier. 2.3 A thermal insulation structure generally consists of an anti-corrosion layer, a thermal insulation layer (insulating layer), a moisture barrier layer, and a protective layer. II. Integrity criteria1. Insulation structure
1.1 The insulation structure is intact; all internal layers are uniform, properly overlapped, with no gaps or deformations. 1.2 The anti-rust layer is intact, tightly sealed, with no damage or corrosion. 1.3 The insulation layer is intact and uniform, without any defects, deformation, moisture absorption, loosening, deterioration, or separation at the seams; it is properly fastened with appropriate tightness. 1.4 The moisture barrier is tight, intact, with no cracking, damage, or water leakage. 1.5 The protective layer is intact and secure, uniform in appearance, with no peeling, water leakage, cracking, curling, flaking or damage; there are also no noticeable irregularities or deformations. 2. The surface of the thermal insulation structure has a uniform color, is free from corrosion, and is level, straight, neat, and aesthetically pleasing. The anti-corrosion coating meets the requirements of HGJ010043 \"Pipeline Coating\". 2.1 Thermal insulation performance 2.2 The thermal insulation effect of equipment and pipelines shall meet the process requirements or design specifications. 2.3 The surface temperature of the thermal insulation structure shall meet the following requirements: 2.3.1 When the ambient temperature does not exceed 25°C, its surface temperature shall not exceed 50℃ ； 2.3.2 When the ambient temperature is greater than 25°C, its surface temperature shall not exceed the sum of the ambient temperature and 25°C. 2.3.3 The surface temperature of the cold insulation structure shall be 1–2°C higher than the local dew point temperature used in the design. 2.3.4 The heat loss shall not exceed the allowable maximum value for heat loss specified in GB4272 \"General Rules for Thermal Insulation of Equipment and Piping\". 3. Archival materials 3.1 The archival materials are complete and intact. The archival materials include: the original completion documents for the thermal insulation structure ； Archival documents regarding changes to the thermal insulation structure during use ； Test and evaluation data on the thermal insulation performance of equipment and pipelines over various periods ； Records of major repairs for insulation of important equipment and pipelines ； Records of the application of new materials, new processes, and new structures for insulation. 3.2 Archive documents should be filled out promptly, clearly, and neatly. III. Maintenance and Inspection 1. Daily maintenance checks 1.1 The insulation structure must remain intact; it shall not be damaged or harmed, nor should anyone step on, tread upon, knock, or hit it. The insulation structures damaged due to work requirements must be restored in a timely manner. 1.2 For the macroscopic inspection of thermal insulation structures, emphasis should be placed on inspecting the following areas. 1.2.1 Expansion joints and expansion gaps ； 1.2.2 Support locations for pipes and equipment ； 1.2.3 Starting and ending points of insulation, planar bends and corners ； 1.2.4 Areas prone to trampling and damage ； 1.2.5 Connection area between old and new insulation layers. 1.3 The visual inspection of the protective layer should focus on the following conditions: 1.3.1 Glass cloth wrapping layer: loosening, cracking, separation of the end caps, failure of coatings or paints, discoloration, loss of luster, moisture permeation, etc ； 1.3.2 Plaster protective layer: cracking, peeling, moisture penetration, etc ； 1.3.3 Metal protective layer: screw connection or snap-off, surface corrosion, bent edges, deformation, etc. 1.4 Before maintenance and commissioning, the insulation of equipment and pipelines shall be inspected individually; they may only be put into use after passing the inspection. 3.2 Regular inspections 1.4.1 Inspections of insulated equipment and pipelines should be carried out once per quarter; any issues found should be repaired or replaced promptly. 1.4.2 A thorough inspection of the insulation on equipment and pipelines should be carried out every year before winter arrives. 1.4.3 The plant shall test the insulation effectiveness of the insulation on the following equipment and pipelines every three years: (1) Insulation on important equipment and pipelines ； (2) Insulation for equipment and pipelines used over the long term ； (3) Insulation for equipment and pipelines with large temperature fluctuations and poor process conditions identified in the process. IV. Maintenance Cycle and Contents 1 Maintenance Cycle 1.1 The maintenance of equipment and pipeline insulation is generally divided into repairs, minor repairs, and major repairs. Its maintenance cycle usually takes place in conjunction with the inspection or maintenance of the equipment and pipelines. 1.2 When the inspection and maintenance of equipment and pipelines are not considered, the maintenance of the insulation structure: the minor and major repair cycles are shown in Table 1. 1.3 When the heat loss at the surface of the insulation structure is too high, failing to meet the process requirements or exceeding the maximum heat loss value permitted by GB4272 \"General Rules for Insulation Technology\", major repairs should be carried out. Its major repair interval is not subject to the limitations in Table 1. Table 1: Repair categories – Maintenance (years), Minor repairs (years), Major repairs (years). Glass cloth wrapping type: 1, 3, 5; Plaster protection type: 1, 3–5, 10; Metal protection type: 1–2, 5–7, 15–20. 2. Repair contents: 2.1 Maintenance. 2.1.1 Repair of locally damaged protective layers ； 2.1.2 Local deformation or loosening of the thermal insulation structure. 2.2 Minor repairs 2.2.1 Includes the scope of repairs ； 2.2.2 Overall painting of the protective layer surface ； 2.2.3 Overall wrapping of the protective layer, overall plastering for repair, or large-scale repair of the metal protective layer ； Update of the insulation layer structure in section 2.2.4. 2.3 Major overhaul: Complete replacement of the insulation structure for equipment and pipelines. V. Maintenance Methods and Quality Requirements 1. General Provisions 1.1 Materials 1.1.1 Common thermal insulation materials include: (1) expanded perlite and its products ； (2) Ultra-fine glass wool and its products ； (3) Asbestos products ； (4) Rock wool and its products ； (5) Aluminum silicate fibers and their products ； (6) Polyurethane foam plastics and their products ； (7) Polystyrene foam products, etc. 1.1.2 Before construction, it is necessary to carefully check whether the properties of the insulation material used, such as its unit weight, mechanical strength, thermal conductivity, operating temperature, fiber diameter, slag ball content, moisture content, flame resistance and fireproofing capabilities, moisture resistance, and physical dimensions, meet the technical requirements specified in the design. The chloride content in the insulation materials used for austenitic stainless steel equipment and pipelines must be within acceptable limits. 1.1.3 Unqualified insulation materials must not be used. Moistened insulation materials that cannot regain their qualified performance after drying must not be used. The moisture content of thermal insulation materials and their products should not exceed 1%. 1.1.4 The materials of the moisture-proof layer and protective layer shall be free from defects such as perforations, cracks, or delamination; metal materials shall be free from defects such as rust or deformation. 1.1.5 Insulation materials must be protected from moisture, water, freezing, damage, and compression deformation during storage, transportation, and on-site installation. Items should be arranged in categories and neatly. 1.2 Insulation work on equipment and pipelines can generally be carried out at temperatures below 65°C, but insulation work for heat retention must be completed before the cold medium is introduced. 1.3 Equipment and pipelines must pass tests for strength, airtightness, installation and fixation, as well as descaling, rust removal, and corrosion protection, before construction can proceed. 1.4 When welding insulation fixings on industrial equipment and pipelines with anti-corrosion coatings and linings, the welding work must be carried out prior to the application of the anti-corrosion coatings and linings as well as pressure testing (including heat treatment). 1.5 Equipment and pipelines that require regular observation, inspection, disassembly, and maintenance (such as creep measurement points, weld monitoring points, manholes, handholes, sight holes, flanges, valves, and pipe fittings) should employ a detachable insulation structure, with the insulation material being the same as that of the main structure. 1.6 The detachable and fixed parts of cold-insulating equipment and pipelines must be sealed. 1.7 The corners of equipment and pipelines shall be provided with closed overlaps to prevent the formation of gaps. 1.8 Accessories such as skirtings, supports, lugs, instrument flanges, brackets, and hangers on equipment or pipelines do not require insulation unless otherwise specified in the design. However, the aforementioned accessories of the insulation equipment or pipes shall be insulated, with a length that is not less than four times the thickness of the insulation layer or extending to the sleepers. 1.9 Gaps should be left on both sides of the flange connection to facilitate bolt removal; one such gap should be 25 mm longer than the length of the bolt. Pipes with sliding contacts and hangers should have gaps to prevent damage to the protective layer and to allow normal expansion and contraction of the pipes. 1.10 Expansion joints and contraction joints shall be provided in the insulation layers, moisture-proof layers, and protective layers of equipment and pipelines as per the design, and the width of such joints shall be as specified. —It is generally 20mm to 25mm. 1.11 The expansion and contraction joints of the insulation layer should be tightly filled and securely tied using soft fiber felt strips, ropes, etc. For expansion and contraction joints in the insulation layer, use moisture-proof materials to seal the ends of the insulation material within these joints; thereafter, fill them tightly with soft foam plastic strips, ropes, etc., or apply foaming adhesive, and then provide additional insulation on the outside of the joints. 1.12 When carrying out outdoor insulation work in rainy weather, rain protection measures should be taken. When the average outdoor temperature is below 5°C or the lowest temperature is below ~3°C, winter construction measures should be employed. 2. Insulation layer 2.1 The construction methods for the insulation layer include bundling, masonry, wrapping, bonding, filling, casting, spraying, etc. The filling method shall not be used for equipment and pipelines that vibrate. 2.2 When using one type of material for construction, if the thickness of the insulation layer is greater than 100 mm and the thickness of the thermal insulation layer is greater than 80 mm, construction should be carried out in layers, with the layer thicknesses being as similar as possible. Except for insulation layers constructed by spraying, casting, and filling methods. When two or more composite insulating materials are used, their thicknesses shall be specified according to the design requirements. 2.3 For insulation layers made of molded products, the seams should not be larger than 5 mm; the seams in the heat-insulating layer should not be larger than 2 mm. The seams within the same layer should be offset from each other, while the seams between upper and lower layers should be offset as well, with the overlap distance between such seams being no less than 50 mm. When using soft cotton or felt insulation layers, lap joints should be employed, with a length of no less than 50 mm. 2.4 The longitudinal joint of horizontal pipes shall not be located within 45 mm above or below the vertical centerline of the pipe. Large-diameter multi-layer insulation products are not subject to this limitation when providing insulation, but should be positioned offset from the vertical centerline of the pipeline. 2.5 For dry joints, mineral wool strips or cut pieces should be used for filling the gaps; for wet joints with mortar, mortar of the same type as that used in the masonry should be used for sealing the joints. There shall be no half-joints or gaps, whether in dry masonry or wet masonry. 2.6 The extension length and installation spacing of the thermal insulation supports shall comply with the following provisions. 2.6.1 The protrusion length of the support member is 10~20 mm less than the thickness of the insulation layer. 2.6.2 The installation spacing for vertical equipment and vertical pipe supports is 1~3 m. 2.6.3 The spacing between hooks is generally 350~600 mm. 2.7 When the support members cannot be welded directly to the equipment, clamps should be used for welding, with a distance between the clamps not exceeding 500 mm. 2.8 When using the bundling method for construction, the spacing between bundles shall comply with the following provisions ； 2.8.1 Rigid products not exceeding 400mm ； 2.8.2 Semi-rigid products not exceeding 300mm ； 2.8.3 Soft felt and pads shall not exceed 200 mm. However, there must be no less than two strips on each product, and they must not be wrapped in a spiral pattern. 2.9 Vertical equipment or vertical large-diameter pipes shall be constructed from bottom to top, and secured using a mesh tied with galvanized iron wire. Insulation for horizontal pipes and small-diameter vertical pipes can be secured using hookless circumferential bundling or hooked mesh bundling. 2.10 For insulation boards, blocks, or bricks constructed using the mosaic method, the joint gaps should not exceed 5 mm; any incomplete mortar fills or damaged blocks should be filled with mortar. During construction, rubber splints or wire can be used for temporary fixation. 2.11 The winding method for installing insulating ropes is only suitable for small-diameter pipes and pipe bundles. When winding, pull tightly to ensure that the loops are arranged closely together. The second layer of winding should overlap the first layer in the opposite direction, and both ends of the rope should be securely tied with galvanized wire. 2.12 Insulation structures constructed by the filling method must have a solid layer to prevent deformation during the filling process. Generally, the metal protective layer is directly used as the solid layer. 2.13 The vertical filling structure shall have a settlement prevention layer to prevent the filler from sinking; generally, hard materials are used for layered construction or bonding at each section of the filler height. 2.14 For bulk granular materials or bulk mineral materials constructed by the filling method, compaction should be carried out in layers, with each layer’s height preferably ranging from 400 to 600 mm. Large-diameter horizontal pipes should be filled in halves within the factory; the pressure applied must be even, and the density must be consistent. The unit weight of the material after filling; 2.14.1 The unit weight of mineral wool is 1.3 to 2.4 times the production unit weight ； 2.14.2 The bulk density of the granular material is 1.2 to 1.4 times the production density. 2.15 After the filling process is completed for the insulated structure, the seams must be sealed and tested for leaks by inflating it. 2.16 Insulation boards and blocks to be installed using the pasting method should be pre-shaped according to the dimensions of the equipment and pipes. Its inner diameter should be slightly larger than the outer diameter of the equipment and pipes, ensuring that the finished insulation material fits tightly against the surfaces of the equipment and pipes. 2.17 The adhesive should be applied evenly, adhered firmly, compressed tightly, and the joints should be sealed properly. The insulation layer installed in an upside-down position should be secured using fixed screws, pins, or self-locking plates. Temporary fixation using rubber bands or steel strips can be employed during construction. 2.18 For construction by the pouring method, a slip form designed according to the shape of the equipment and pipes must be used, or a fixed form made of a metal protective layer. Sliding mold requires a smooth surface on the slide plate, tight joints, accurate dimensions, stable supports, and an inner coating of release agent. The length of the steel slip form for the insulation layer of the pouring pipeline should be 1.2 to 1.5 meters. 2.19 When applying the coating method, the thickness of the coating layer should be determined in advance, and then application should be carried out from bottom to top. The spray layer should be uniform, without any depressions or excessively protruding areas; its flatness and appearance must meet the required standards. 2.20 For the pouring or spraying of polyurethane foam plastics, trial pouring or spraying should be carried out in accordance with the mixing process and spraying procedures; formal construction can proceed only after approval is obtained. 2.21 When using foam glass products for insulation, a wear-resistant agent should be applied between the products and the surfaces of equipment and pipes, as well as between the products themselves. 3. Rust-proof and moisture-proof layers 3.1 For carbon steel equipment, pipes, and their accessories that require insulation, it is necessary to remove rust, grease, and other contaminants from their outer surfaces before insulation is applied. After that, two coats of priming paint or rust-proof paint should be applied as a rust-proof layer. Equipment, pipelines, and their fittings made of stainless steel, non-ferrous metals, and non-metallic materials do not require an anti-corrosion coating. 3.2 The surface of the insulating layer where the moisture barrier is to be installed shall be cleaned, kept dry, and made smooth and uniform. There shall be no sharp corners, pits, or sanding. 3.3 The installation of the moisture-proof layer should be carried out immediately after the installation of the insulation layer, to prevent the insulation layer from getting wet or exposed to rain and snow. 3.4 The moisture barrier is generally made of asphalt mastic or a composite of modified asphalt and glass fiber cloth. The construction sequence is as follows: 3.4.1 A layer of petroleum asphalt mastic or modified asphalt with a thickness of 3 mm ； 3.4.2 One layer of medium-alkali coarsely textured plain-weave glass cloth with a thickness of 0.1~0.2 millimeters ； 3.4.3 Spacing between zinc-coated wire or steel strip ties: 300 mm ； 3.4.4 Thickness of petroleum asphalt mastic or modified asphalt layer: 3 mm ； 3.4.5 The moisture-proof layer used for insulation can also be covered with a layer of asphalt felt, and tied together from the outside using galvanized iron wire or steel strips at intervals of 300 mm. 3.5 The technical requirements for the construction of the moisture barrier are as follows. 3.5.1 The application of asphalt mastic or modified asphalt should be thorough, with a uniform thickness and smooth surface. 3.5.2 Glass cloth should be applied alongside the asphalt layer as it is laid. The longitudinal and circumferential seam overlaps shall be no less than 50 mm, with the seam edges facing downward, and the overlapping seams shall be securely bonded. The pasting method can be spiral winding or flat laying. 3.5.3 The overlapping method shall be used for the installation of bituminous felt damp-proof courses. The longitudinal and circumferential seam overlaps shall be no less than 50 mm, with the seam edges facing downward. The longitudinal seam of horizontal pipes shall not be within 45 mm above or below the vertical centerline of the pipe. 3.5.4 The ends of the binding wire or steel strip shall be flattened, but must not puncture the moisture barrier. 3.6 The moisture-proof layer at pipeline valves, supports, hangers, or equipment mounts shall be installed in accordance with relevant technical requirements. 4. Protective Layer 4.1 For the metal protective layer, galvanized thin steel sheets, aluminum alloy thin sheets, and ordinary thin steel sheets with anti-corrosion treatment on both the inner and outer surfaces can be used. 4.2 When installing the metal protective layer, it should be placed tightly against the insulation layer or moisture barrier; however, the connecting screws or studs must not damage the underlying moisture barrier. 4.3 Metal protective layers can be spliced or lapped, or even interlocked. The overlap or splice length should be no less than 50 mm; at elbows, it should be 75–100 mm. When overlapping or splicing, the joint should face downward. The metal protective layer for insulating roof equipment should have a drainage slope of 1–2%. 4.4 The fixing spacing for connecting screws or bolts is approximately 200 mm; however, there must be no fewer than 4 screws/bolts per joint. 4.5 At all locations in the insulation layer where expansion gaps are provided, metal enclosures should also be installed. 4.6 There are several types of fabric protective layers: 4.6.1 Vinyl acetate emulsion for bonding glass fabric ； 4.6.2 Using asphalt or modified asphalt to bond asphalt shingles to glass cloth ； 4.6.3 Polyester resin bonding glass cloth ； 4.6.4 Aluminum foil glass cloth or aluminum foil kraft paper ； 4.6.5 Vacuum aluminum-coated composite materials. All the aforementioned materials must be inspected and found satisfactory before use. 4.7 The starting and ending points of the fabric wrapping layer should be secured with galvanized iron wire or steel strip. The overlap seam of the glass cloth wrapping shall be no less than 50 mm, while the overlap seam of the aluminum foil wrapping layer shall be no less than 30 mm; these seams shall be sealed with pressure-sensitive tape. 4.8 The bonding process using vinyl acetate emulsion shall not be carried out in outdoor areas, humid environments, or at ambient temperatures below 8°C. 4.9 The plaster mortar for the finishing layer shall meet the following requirements: 4.9.1 Its bulk density shall not exceed 1000 kg/m³. 4.9.2 Compressive strength shall be not less than 784 kPa (8 kgf/cm²). 4.9.3 The loss on ignition (including organic matter and combustibles) shall not exceed 12%. 4.9.4 After drying (in a cold state), it is less prone to cracks, peeling, and similar issues, and possesses waterproof properties. It must not cause corrosion to metals. 4.10 Before construction, a wire mesh should be wrapped around the exterior of the insulation layer or vapor barrier for the finishing protective layer; this wire mesh should then be secured using galvanized wire. The spacing between the ties is generally 250–350 mm. 4.11 Except for the protective layers of galvanized thin steel sheets and aluminum sheets, all other protective layers shall be painted with oil-based paint. Coating is usually applied 2 to 3 times, and the color of the oil shall comply with the provisions of HGJ010043 \"Pipeline Painting\". 5. Quality Requirements 5.1 In addition to complying with the relevant provisions mentioned above, the construction quality of the thermal insulation structure shall also meet the following requirements. 5.2 The quality requirements for the insulation layer are as follows: 5.2.1 The joints in the block insulation layer must be fully filled with mortar, or filled with mineral wool. The seam width shall not exceed 5 mm, and in some areas it shall not exceed 7 mm. 5.2.2 The insulation block layers shall be bonded tightly, and the joint gaps shall not exceed 2 mm. 5.2.3 The allowable deviation for the insulation layer thickness is shown in Table 2. Table 2 Permissible deviations for insulation types, in mm: Insulation layer – +5; Soft, hard, and semi-hard products – +10 to –5; Filled, poured, and sprayed coatings – +10%. 5.2.4 Permissible deviation for the bulk density of the insulating layer: (1) For hard and semi-hard products, it is +5% ； (2) Soft layers and filling, spraying, and casting layers are +10%. 5.2.5 The allowable deviation for the width of expansion and contraction joints in the thermal layer and protective layer is preferably checked using a feeler gauge at +5mm. 5.2.6 The quality requirements for the moisture-proof layer are as follows: (1) The surface shall be smooth, and all joints and layers shall be tight, without defects such as pores, bubbles, warping, delamination, cracking, or mechanical damage. The flatness deviation of the moisture-proof layer with a metal protective layer shall not exceed 5 mm. (2) The total thickness of the bituminous mastix or modified bitumen glass cloth moisture barrier shall not be less than 5 mm. . 5.2.7 The flatness of the protective layer shall be checked using a 1m straightedge, with the allowable deviation as specified in Table 3. 5.2.8 The visual inspection requirements for the protective layer are as follows: (1) The surface of the plaster layer shall be smooth with neat contours, and there shall be no looseness, cracks, or exposed wire ends. (2) The wrapping layer and metal protective layer shall be even and neat, without any loosening, flanging, warping, or obvious pits. Its lap joints should be uniform; the joints of the metal casing should be perpendicular to the direction of the pipeline, and the longitudinal joints should form neat straight lines. (3) The painting of the insulation structure should be even and neat, with accurate colors and a pleasant finish; there should be no bubbles or sagging. Table 3 Allowable deviations for insulation types, in mm: Finish coating and wrapping layer – 5; Metal protective layer – 4; Pipes in buried or inaccessible trenches – no inspection required. VI. Acceptance of maintenance work 1. Interim inspections: During the maintenance process, the competent authority should carry out necessary interim inspections and issue verification documents for each stage of work as well as key areas, in order to address any quality issues that may arise during construction promptly. Those who fail the intermediate inspection shall not proceed to the next stage of work. 2. Final acceptance 2.1 The handover and acceptance should be carried out promptly upon the completion of the thermal insulation work. At the time of acceptance, the major repair work must submit documentation for handover inspection, and if necessary, tests on the insulation performance must also be conducted. When maintenance and minor repair work are completed, delivery documents need not be submitted; however, strict quality control must be maintained, and signing procedures for acceptance must be followed. 2.2 The documents required for the handover and acceptance of the major repair work include: 2.2.1 Specifications for the insulation materials and relevant certification documents (or physical and chemical property test reports) ； Records of concealed works and intermediate inspections ； Construction mixtures for pouring and spraying insulation layers, as well as technical performance test reports ； Mixing ratio of the plaster material for the finishing protective layer and test report on its technical properties ； Design change order and material substitution notice ； Summary table of completion for adiabatic projects. 2.2.2 Insulation works for which thermal insulation performance tests are conducted shall also include the results of those tests. VII. Safety Precautions for Maintenance and Inspection 1. Safety Precautions for Maintenance and Inspection 1.1 The maintenance, inspection, and testing of insulation work shall be carried out in accordance with relevant safety regulations regarding high-altitude work in factories, electrical lighting, construction in different seasons, the setup and dismantling of scaffolding, as well as oxygen content and toxic gas analysis; reliable safety measures must be taken. 1. 2 When inspecting or testing insulated high-temperature equipment and pipelines, measures should be taken to prevent burns. 2. Safety precautions for maintenance 2.1 At the maintenance site for insulation work, in addition to complying with the factory’s relevant safety regulations, the following safety measures must also be observed. 2.2 Operators of insulation work should wear daily protective equipment. When working with fiber-containing, dusty, toxic, and corrosive insulation materials, protective work clothing, protective (gas-proof) masks, dust caps, safety goggles, protective gloves, and protective shoes should be worn, in addition to having available protective medications and equipment. 2.3 Upon completion or suspension of construction, the tools and equipment as well as the construction site should be cleaned thoroughly, and flammable and toxic materials should be placed in designated areas. 2.4 Temporary supports should be removed only after the fixed components have been securely installed. 2.5 When tightening the wire used for securing the holes, do not use excessive force to prevent it from breaking and causing injury due to rebound. 2.6 When working with insulation materials that contain fibers or dust, the following requirements must be followed: 2.6.1 When transporting bulk materials at heights, they must be carried in bags, baskets, or boxes; they must not be lifted using ropes alone. 2.6.2 During the sewing of fiber cotton felt, care should be taken to prevent steel needles or wires from causing injury. 2.6.3 The work site should improve the operating environment to prevent dust and harmful gases from spreading. The maximum allowable concentration of harmful gases in the dust phase shall comply with the provisions of the **current ‘Health Standards for Industrial Plant Design’. 2.7 The safe handling of flammable, volatile, toxic, and corrosive materials shall comply with the following provisions. 2.7.1 Flammable and volatile substances must be kept away from direct sunlight, and areas where they are stored must be free from fire, sparks, and high temperatures. 2.7.2 Toxic and corrosive liquids must not be stored at high elevations; the containers must be sealed, and immediate action must be taken if any leaks are detected. 2.7.3 In workplaces where there is contact with irritating substances and a risk of burns, flushing facilities should be available. 2.7.4 When preparing the asphalt binder, materials should be added in batches, melted at a low temperature, and mixed thoroughly. The level of the melted material should not exceed two-thirds of the container’s capacity to prevent overheating, ignition, or burns. Its heat mixing temperature must not exceed the initial boiling point of the diluent oil used. Tools for applying asphalt must not be soldered. 2.7.5 When preparing the binder with benzene or gasoline, it should be added slowly to the binder, and the preparation must be carried out away from open flames. 2.7.6 When cutting foam plastic products with a resistance wire, the voltage must not exceed 36 volts. 2.8 It is strictly prohibited to point the spray nozzle at people during spraying operations. If a clogged nozzle is detected during construction, the machine should be stopped first, and the supply of fluid should be halted before the nozzle is inspected and repaired. 2.9 Before entering the trench for work, oxygen levels and toxic gas levels must be analyzed; entry is permitted only if the results are satisfactory. Unsafe objects or facilities within the trench must be removed, and adequate lighting must be in place before work can proceed. 2.10 There should be no fire-fighting equipment at the construction site. 2.11 There shall be shower facilities and locker rooms dedicated to the operators. 2.12 Construction workers should have regular health check-ups.