Safety nets are a type of personal protective equipment used to prevent fall injuries. They have a wide range of applications, primarily for various high-altitude operations. Fall hazards from heights often occur on scaffolding, rooftops, windows, in hanging structures, deep pits, and deep trenches. The severity of fall injuries varies depending on the distance of the fall, ranging from minor disability to death. The protective principle of safety nets is as follows: horizontal nets act to block falling people and objects, avoiding or mitigating injuries from falls and impacts; vertical nets prevent people or objects from falling. The net's strength must withstand the weight and impact distance of a person or carrying tools falling, along with the longitudinal tensile force and impact intensity.
Quality Inspection of Safety Nets
Safety nets are special personal protective equipment involving national property and personal safety. Their product quality must be inspected and approved by a nationally designated supervision and inspection department, and a production license must be obtained before production can commence. Each batch of safety nets must have an inspection report from the supervision and inspection department. Each safety net should have a certificate of conformity from the national supervision department and a certificate of conformity from the company's own inspection attached to it in different locations. Simultaneously, signage should be provided, with permanent markings including: manufacturer's name, manufacturing date, batch number, materials, specifications, weight, and production license number.
Safety nets are classified into horizontal nets (P), vertical nets (L), and close-mesh safety nets (ML). Safety nets mainly consist of edge ropes, tie ropes, reinforcing ropes, and net ropes. Close-mesh safety nets consist of the net body, loops, edge ropes, and additional tie ropes. The physical and mechanical properties of safety nets are the main indicators for judging their quality. These include: the breaking strength of edge ropes, tie ropes, net ropes, and reinforcing ropes. Close-mesh safety nets mainly have the following properties: breaking strength, elongation at break, seam tensile strength, tear strength, penetration resistance, retention rate of breaking strength after aging, strength of open loops, and flame retardant properties. Both horizontal and vertical nets should have impact resistance. Vertical nets cannot replace horizontal nets; the choice between horizontal and vertical nets should be determined based on construction needs and load height. Horizontal safety nets require greater load-bearing capacity than vertical safety nets, use more materials, and are heavier. Generally, horizontal safety nets weigh over 5.5 kg, and vertical safety nets weigh over 2.5 kg.
Safety nets are primarily used in open-air work areas. Therefore, they must be weather-resistant. Weather-resistant materials mainly include nylon, vinylon, and polyester. The materials used in the same net should be identical, with a wet-to-dry strength ratio greater than 75%, and the total weight of each net should not exceed 15 kg. The afterflame and smoldering time of flame-retardant safety nets must not exceed 4 seconds.
Horizontal safety nets should be at least 3 m wide, and vertical and close-mesh safety nets should be at least 1.2 m wide. The length of the tie ropes should be at least 0.8 m. The spacing between tie ropes should not exceed 0.75 m. For close-mesh safety nets, the spacing between tie ropes should not exceed 0.45 m, and the distance between reinforcing ropes should not be too small, generally specified as above 0.3 m. Safety nets can be divided into hand-woven and machine-woven types. Mechanical knotting can be divided into knotted knotting and knotless knotting. Generally, the strength of knotless net knots is higher than that of knotted net knots. Knots and joints must be firmly fixed and not moved to avoid increasing the mesh size and uneven side lengths. These issues will lead to stress concentration, eventually causing the net rope to break.