The Life Safety Code is the most widely used source for strategies to protect people based on building construction, protection, and occupancy features that minimize the effects of fire and related hazards.
The 2018 edition of NFPA 101 Life Safety Code details requirements that healthcare facilities such as hospitals, ambulatory, long-term care, nursing home and senior living centers must comply with as they relate to surface mounted objects. Sections 22.214.171.124 and 126.96.36.199 discuss the 4 inch noncontinuous projection requirements.
The 2010 ADA Accessibility Guidelines (ADAAG) have two heights for installing protruding objects on walls. The upper height is 80 inches above the walking surface to avoid a head injury from running into the object. The lower limit is 27 inches above the walking surface. This means that any protrusion that extends to a point 27 inches or less from the walking surface complies with the ADA rules regarding protrusions from walls. This rule is intended to accommodate the sight-impaired population.
A sight-impaired person with a cane can detect a protruding object mounted on a wall with a cane and walk around it. An extinguisher with the bottom at 27 inches or less off the floor can be detected with a cane. Installing the extinguisher hanger so that the bottom of the extinguisher is 27 inches or less from the finished floor is ADA compliant.
NFPA 101 has similar rules around objects that are surface mounted, including fire extinguishers, AED machines, hand sanitizers, etc. The specific sections can be found here:
Some of the content from this article comes from the Fire Equipment Manufacturer’s Association article on ADA and NFPA 101 Wall Projection Rules for Mounting Extinguishers.