Jobs are sedentary if walking and standing are required only occasionally and all other sedentary criteria are met; vocal communication is required to express or exchange ideas by means of the spoken word, and to convey detailed or important instructions to others; hearing is required to respond to spoken words, to receive and understand information, and/or to make fine distinctions in sound; visual acuity is required for preparing and analyzing written or computer data, operation of computers, machines, or equipment, determining the accuracy and thoroughness of work, and observing general surroundings and activities. The employee primarily works in a secure communications center with prolonged sitting, continuous use of computers and communications equipment, frequent radio and telephone communications, rotating shifts as assigned, and exposure to stressful emergency situations requiring sustained concentration.