I'd always had this hunch! The bus recording was supposed to be 安全 but why did it sound like 安前.
Then I got affirmation from 《成都方言》
刘前进
此词源于《刘全进瓜》的古典故事,即与瓜傻同义,便指傻瓜。又由于地域读音关系,“前”与“全”不分,此词又为“刘全进”。歇后语:“~——瓜!”
Specifically: “前”与“全”不分.
This, though, is the only evidence or documentation/reference I have come across talking about this phenomenon.
What other references or documentation exist talking about “前”与“全”不分 or 全 being pronounced qian in Southwestern Mandarin, or more specifically Sichuanese/Chengduese?