Can the height and mesh size of plastic safety fences effectively protect children or pets?

Regarding the protective effect of plastic safety warning net fences on children or pets, a comprehensive assessment needs to be conducted from multiple dimensions such as height, mesh size, structural strength, and usage scenarios. Here are the key analyses: 

Is the height sufficient?
Child protection:
Very young children (1-3 years old): A standard fence of about 1 meter may be temporarily effective (requiring parental supervision), but it cannot prevent children with strong climbing abilities.
Preschool children (3-6 years old): The standard height (usually 1-1.2 meters) is insufficient for protection. Children in this age group have the ability to climb and are prone to jumping over.
School-age children (over 6 years old): The ordinary fence height has almost no protective effect.
Recommendation: The height of the protective fence specifically designed for children should be at least 1.5 meters or more, and the top design should increase the difficulty of climbing (such as inward inclination).
Pet protection:
Small dogs/cats: A height of 1 meter may prevent some small dogs, but has limited effect on cats that are good at jumping or small dogs (such as terriers).
Medium and large dogs: The ordinary height is completely ineffective. Large dogs can easily jump over or knock down.
Recommendation: The height of the pet fence needs to be customized according to the size and jumping ability of the pet (usually 1.2 meters or more), and ensure the structure is stable. 
Conclusion: Standard plastic safety fences (approximately 1 - 1.2 meters in height) offer relatively poor protection against children who can climb or large-sized pets. 

2. Is the mesh size safe?
Risk of entrapment:
If the mesh size is larger than 9cm × 9cm, there is a risk that a child's or pet's head or limbs may get trapped (especially for infants).
Pets may try to squeeze through the mesh, resulting in their bodies getting stuck or escaping.
Assistance for climbing:
Large mesh holes may be used as footholds, making it easier to climb.
Visual and psychological deterrence:
A mesh that is too large will weaken the visual barrier effect and reduce the restraining power over the behavior of children/pets. 
Conclusion: The mesh size should be less than 9cm × 9cm (ideally ≤ 5cm) to reduce the risk of getting stuck and decrease the possibility of climbing. 

3. Other Key Factors
Structural Stability:
If the plastic fence is lightweight and the foundation is not firmly fixed, it may be easily shaken by children or knocked down by pets. It is necessary to ensure a stable base (such as adding counterweights or burying deeply for fixation).
Material Strength and Durability:
Polyethylene (PE) has less impact resistance than metals. Long-term exposure to sunlight may cause it to become brittle and reduce its protective effect. It is necessary to choose thicker and UV-resistant models.
Top Design:
Flat-top fences are easy to climb. Designs with sharp spikes or inward slopes can enhance the protective effect.
Warning Function ≠ Physical Protection:
The warning color of the fence (yellow and black / red and white) is mainly for adults and has no substantive restraint effect on children or pets. 

4. Applicability in Different Scenarios
Temporary isolation in low-risk areas (such as construction warnings): Can meet basic needs, relying on adult supervision to keep children/animals away.
Medium to high-risk areas (such as pools, lanes, and areas near dangerous machinery): It is not recommended to solely rely on plastic fences to protect children/pets. Higher specification protective facilities (such as metal fences, encrypted mesh) should be combined.
Specialized child/pet care: Must choose products specifically designed for this purpose (with heights meeting safety standards, small mesh sizes, and anti-climbing structures), and be accompanied by adult supervision. 

Summary of Recommendations
1. Ordinary plastic safety fences (1-1.2 meters high, with large mesh) cannot reliably protect the safety of children or pets, especially for children over 3 years old and medium-sized or larger pets.
2. If the protected objects are children or pets:
Choose dedicated protective fences: height ≥ 1.5 meters (for children) / ≥ 1.2 meters (for pets), mesh size ≤ 5 cm.
Ensure the structure is stable (weight the base / bury deeply for fixation).
Give priority to anti-climbing design (no horizontal bars, top inwardly inclined).
Do not replace adult supervision! The fence is an auxiliary tool and cannot completely replace guardianship.
3. In dangerous areas (such as roads, deep water areas), more sturdy protective facilities (such as metal fences) should be used. Plastic fences can only serve as supplementary warnings. 
Safety is no trivial matter, especially when it comes to children and pets. When choosing protective facilities, one must adhere to the highest safety standards and combine continuous supervision to minimize risks to the greatest extent possible.