The reason Mark was hoping the burn victim was exposed to hydrochloric acid and not hydrofluoric acid is because of it's toxicity. Both are strong acids that can cause severe chemical burns, but hydrofluoric acid has the added complication of being a potent contact poison. When it comes into contact with skin it causes severe burns and the fluorine in the acid is rapidly absorbed through the skin causing fluorine toxicity. When absorbed into the bloodstream fluorine reacts with the calcium in the blood which can cause cardiac arrest, it also starts bonding with the calcium in the tissues causing hypocalcemia. Treatment involves applying calcium gluconate cream to the affected areas, which bonds to the fluorine atoms preventing them from bonding to calcium in the blood stream and tissue; IV calcium is also given in cases of severe burns to help offset calcium loss systemically. Burns with a surface area larger than 25 square inches will cause serious systemic toxicity and are often fatal. As Mark states at the time of this episode's filming there were no other known treatments for serious hydrofluoric acid burns, however research done around 2015 showed that applying hexafluorine fluid to hydrofluoric acid burns immediately after exposure improved patient outcome greatly. A short time later a hexafluorine solution specifically for hydrofluoric burns was developed, when applied to exposed areas of the skin immediately after it is able to neutralize both the positive acid ions and the negative fluorine ions on contact, it was clinically proven to neutralize fluorine 100 times more effectively than calcium gluconate. Hexafluorine solutions are now kept in all work areas that use hydrofluoric acid and has severely improved patient outcomes from exposure.
The initial script for the episode makes explicit what many of Carol Hathaway's interactions with Doug before the final scene strongly imply: she was treating him with spite and hostility in the "hope" that he would fight back and she would have an excuse to break up with him. Julianna Marguiles hated this idea and bluntly told the writer that she wouldn't play a breakup scene opposite George Clooney and for him to have a new idea. That idea ended up being the confirmation of love between Doug and Carol that ended the episode.
The genesis of the Michael Rapaport-starring central story came when Jack Orman compiled several dramatic elements of life and death stories that ER had already done (including a person who were in good health at the start of a day and dead by its end, patients learning to their horror that they were going to die in the hospital, bonding between a terminal patient and a hospital worker, and a patient reflecting on his or her life as their demise nears) and put them all together into the Paul Caterna storyline.
Julianna Margulies (Carol Hathaway) & Howard McGillin (Herrguth) also worked together on two episodes of The Good Wife (2009) as Alicia Florrick & Lloyd Garber respectively.
Victor Williams (Roger McGrath) & Julianna Margulies (Carol Hathaway) also worked together on episode 6.9 Sticky Content (2014) of The Good Wife (2009) as Carter Greyson & Alicia Florrick respectively.