What does the acronym osh a stand for

  Assuming you are referring to the acronym; "OSHA" ;

"OSHA" stands for:  the "Occupational Safety and Health Administration" ; 

        [the U.S.A. governmental regulation and enforcement agency].

Note:  You asked:  "What does the acronym OSH a stand for" ?

I assumed you meant, "OSHA" — since you did type "OSH a" ; and I do know about "OSHA" .  Also, I considered the fact that this question was posted in the "Health" category—and appropriately so!
     This "typographical error" is "no big deal" your part; rather, I simply want to point this out—and it is a good thing to be familiar with "OSHA" —or, at the minimum, know what "OSHA" stands for—and is!
 
However; you MAY have meant to asked:

     → " What does the acronym "OSH" stand for? " ;

          → Note that both questions are valid—and both arerelevant to the "Health" category in "" !

I share start with the acronym—" OSHA " :
              Many employers, as well as some employees, in the mainstream U.S.A—and virtually all of the employees in management positions — [have heard of/ are familiar with] — "OSHA" (or, "O.S.H.A.") — especially those who work with food, chemicals, and machines that could be hazardous—
          {Note: These industries include: manufacturing, fast food, grocery stores, those that require protective gear (from HAZMAT to "laboratories"; to those industries/jobs that require safety googles—and/or other protecting equipment;  those that require approved chemicals for use in cleaning in the workplace & dealing with clean-up of "debris/spills" or even "blood-borne pathogen material" (e.g., even the smallest amount of "blood" from a kid who stubs her toe in the grocery store while wearing "flip-flop sandals"—& some portion of blood gets on the floor —is treated as a "potential blood-borne pathogen" & requires OSHA-approved clean-up procedures / including a designated "blood-borne pathogen kit)".

      Now, in practice, we are aware that there are not only OSHA guidelines that lack adherence—but OSHA regulations/codes/laws that lack adherence as well.  To cite just ONE example:
       → The "blood-borne pathogen kit" (with extensive required procedures) is not always used for small amount of blood on the floor) — but technically, this would be a violation of "OSHA"—and could result in a huge fine to the EMPLOYER if discovered! 
     → {not to mention potential violations of state health codes, etc.)

     →    Now, for the "second question"—

                 →  What does "OSH" stand for? :

               " OSH " stands for "occupational safety and health" .
OSH ; also known as "occupational health" or "workplace health and studies" is a field or integrated discipline; or even "approach"; that focuses on safety of humans in work and work-related settings of all kinds; and is used worldwide.  There are multiple organizations worldwide that use OSH;  including one in the U.S.A that works directly with "OSHA" (see above).  In the U.S.A., physicians can get board-certified in OEM (occupational and environmental medicine). 
               The "OSH" school of thought strives to prevent workplace injuries and to identify factors and recurring themes (using risk management; assessing hazards among various industries); and considers appropriate contigency planning and education.