HB 457 amends Section 505.017 of the Health and Safety Code to establish a toxic chemical emergency alert system requiring state agencies to notify the public within 30 minutes of determining a chemical release poses a substantial threat to human health or the environment. Alerts must continue until the threat subsides and include information on affected areas, the chemicals involved, symptoms requiring medical treatment, and instructions to minimize exposure. The state emergency response commission is responsible for developing and maintaining the system, which will use methods such as reverse 911 calls, text messages, emails, and social media, with alerts provided in both English and Spanish. Residents can register for preferred notification methods or opt out of alerts. The system will be reviewed and updated every four years. The act takes effect on September 1, 2025, and the alert system must be operational by January 1, 2027.