The Association for the Advancement of Medical Instrumentation (AAMI) has made standards freely accessible for PPE, including masks, gloves, gowns, as well as ventilators. Additional guidance is provided for other related equipment like clinical thermometers, infusion pumps, and sterilization and disinfection. 
https://www.aami.org/news-resources/covid-19-updates/coronavirus-resources-for-the-field

The American National Standards Institute (ANSI) has created a portal, Freely Available ISO and IEC Standards to Help Address COVID-19 Crisis, that includes (as of 4/14/2020) 36 international standards covering medical equipment and devices – including ventilators and respiratory equipment; protective clothing used in health care settings; and business continuity management, security, and resilience.

The standards are accessible in read-only format at no cost during the crisis; additional standards may be added in the future. To access the portal, users must accept the license agreement and register. Once registered, users can return to the portal via https://asc.ansi.org.

https://www.ansi.org/news_publications/news_story?menuid=7&articleid=27ba33a0-7482-47c5-b3a7-faa8a55518eb

ASTM International is providing no-cost public access to important ASTM standards used in the production and testing of personal protective equipment - including face masks, medical gowns, gloves, and hand sanitizers - to support manufacturers, test labs, health care professionals, and the general public as they respond to the global COVID-19 public health emergency. 
https://www.astm.org/COVID-19/

 The European Commission is offering free access to 11 standards developed by CEN and potentially 3 additional ones developed jointly with ISO that are made available cover common filtering masks, medical gloves, and protective clothing. The press release lists all 11 standards (and the 3 potential standards) as well as provides information on how to access them. https://ec.europa.eu/commission/presscorner/detail/en/ip_20_502

 The Institute of Electrical and Electronics Engineers (IEEE) has identified articles and standards from the IEEE Xplore digital library that may help researchers. All content in this collection is now free to access for the duration of the global health crisis, with additional rights for all types of reuse, including full text and data mining, and analysis.

To access documents, click on the "View Documents" button; to narrow by standards, select Standards from above the search results set. 
https://spectrum.ieee.org/free-access-to-thousands-of-covid19-research-documents

The International Organization for Standardization (ISO) has compiled a list of standards to support global efforts in dealing with the COVID-19 crisis. They are freely available in read-only format. They cover PPE products, medical devices including ventilators and other medical electrical equipment.
https://www.iso.org/covid19-members

Several other academic institutions have put together Guides related to standards and COVID-19. Please check these for additional information and resources.