The phrase "a safe field" is correct and usable in written English.
It can be used in contexts where you are referring to an area or domain that is secure or free from danger, whether literally or metaphorically.
Example: "The children played in a safe field, away from the busy roads and potential hazards."
Alternatives: "a secure area" or "a protected space."
While field measures of muscular power, such as vertical jump have been validated and widely used among athletes and young adults, a safe field measure for assessing muscular power among older adults has not previously been devised.
Do not work solely from photographs; if your field guide provides photographs, but only scant descriptions, it is not a safe field guide to use.
It was probably a safer field for me to go into than astronomy or psychology".
For the design of most technical systems a desirable safe field of use is calculated from systems technical constraints, and expectations of human capacities and limitations.
The only hospital in the city was bombed with several mortar shells in 2012 and the volunteering doctors tend to work in unequipped basement as what they could call an almost safe field hospital.
Resources for a well-equipped and safe field experience.
The problem with these cases is that the legal definition of "obscene," one that is obviously not a universally held definition, does not provide a safe playing field for controversial filmmakers who don't share the views of conservative anti-obscenity prosecutors.
So far, the main alliances with the left have been in the relatively safe field of foreign policy.
Performance incursions outside the safe field are then limited by means of hard-protections, instructions, education, and regulations.
Keeping the effects localized could enable safe field trials and allow each community to make decisions about their own shared environment, avoiding international disputes.
However, once in service, the socio-technical conditions of work create conditions for performance to migrate and stabilise outside the expected safe field of use.
