Final answer:
To protect bystanders' vision, announce a warning such as "Shield your eyes!" or "Cover!" before starting activities involving intense light, ensuring they use proper eye protection like welders' goggles or eclipse glasses.
Step-by-step explanation:
To avoid starting an arc in front of someone with unprotected vision, particularly in contexts such as welding or observing solar phenomena, it's essential to prioritize eye safety. Before engaging in activities that involve intense light or thermal energy, it's common to announce a warning such as "Shield your eyes!" or use a phrase specific to the context, for example, welders might say "Cover!" before starting an arc. This ensures that anyone in the vicinity can protect themselves by looking away or using proper protection like welders' goggles or specially designed eclipse glasses to prevent retinal damage.