This is the 16470th most frequent Russian word.
рятувальників
"Рятувальників" is Ukrainian, not Russian, and translates to "rescuers" in English.
In this sentence, 'рятувальників' is used in the accusative plural form to denote the people who are rescue workers being called for help.
Рятувальників звали на допомогу під час пожежі.
The rescuers were called for assistance during the fire.
Here, 'рятувальників' is in the genitive plural form, indicating the possession of the dogs belonging to the rescuers.
Суки рятувальників навчені шукати людей під завалами.
The rescuers' dogs are trained to search for people under rubble.
In this context, 'рятувальників' is used in the genitive plural to indicate the topic or subject of the books, which is rescuers.