What is one requirement for sign posting after a chemical treatment?

The requirement for sign posting after a chemical treatment emphasizes that the sign must be sturdy and noticeable. This is crucial because the purpose of the sign is to alert individuals to the recent application of chemicals, indicating that they should avoid the treated area for safety reasons. A sturdy sign ensures it remains in place despite environmental factors, such as wind or rain, while its noticeable design draws attention effectively to the warning. The visibility and durability of the sign are paramount in ensuring that the message is communicated clearly and remains effective throughout the treatment's necessary precautionary period.

The other options, while they may have some relevance in different contexts, do not align with the primary needs for safety and clarity in post-treatment notification. A temporary sign may not provide sufficient warning if it is removed too quickly, and electronic signs may not be practical or necessary in all situations. Biodegradable materials, while environmentally friendly, do not guarantee the visibility or durability required for effective communication in this context.