Occupational Health and Safety Code 2009 Schedule 10. S10 - 1. Schedule 10 Fire Extinguishers and Minimum. Separation Distances. Table 1 Fire extinguisher required based on quantity of explosive.
http://www.amsaonline.org/resources/OHSSchedules/OHSCode_Sch10.pdf
(3) Portable fire extinguishers shall be subjected to an annual maintenance check. Stored pressure extinguishers do not require an internal examination. The employer shall record the annual maintenance date and retain this record for one year after the last entry or the life of the shell, whichever is less.
https://www.dir.ca.gov/title8/6151.html
From the distances point of view, you are right NFPA 10, appendix E is clear on this, but remember that it is supposed that area and distances only apply for common buildings. I will suggest to go conservative and think of placement on strategic areas.
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I am having some trouble with regard to the maximum distance between two fire extinguishers. The books talks about the travel distance of 75 feet, NFPA 10 2007. Ed. page 11 Table 6.2.1.1.
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(6) The employer shall distribute portable fire extinguishers or other containers of Class D extinguishing agent for use by employees so that the travel distance from the combustible metal working area to any extinguishing agent is 75 feet (22.9m) or less.
https://www.dir.ca.gov/title8/6151.html
RE: Fire Extinguisher Placement. but if you are standing in the middle of 150 feet (at 75 feet)you have 75 feet travel distance in between each other. if you had a 150 feet corridor. in that if you are at either end of the corridor you would only have to walk 75 feet max to get to the fe.
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Where extinguishers are provided but are not intended for employee use and the employer has an emergency action plan and a fire prevention plan which meet the requirements of Sections 3220 and 3221 then only the requirements of Sections (e) and (f) of this Section apply. (b) Exemptions.
https://www.dir.ca.gov/title8/6151.html
(2) The employer shall distribute portable fire extinguishers for use by employees on Class A fires so that the travel distance for employees to any extinguisher is 75 feet (22.9m) or less.
https://www.dir.ca.gov/title8/6151.html
Think if you have a building where the exit stairs and elevators are in the center of the building, in that case there is no problem to install just one extinguisher in the center of the area if it covers the area and travel req. as cdafd tells.
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(4) The employer shall distribute portable fire extinguishers for use by employees on Class B fires so that the travel distance from the Class B hazard area to any extinguisher is 50 feet (15.2m) or less.
https://www.dir.ca.gov/title8/6151.html
what is the minimum distance between fire extinguishers
A fires so that the travel distance for employees to any extinguisher is 75 feet  or 22.9 meters or less.