The National Weather Service declares a heat emergency when the heat index, a combination of the air temperature and humidity, equals 108-degrees for 2 or more consecutive days.
City of Houston's EMS director Dr David Persse says a heat index of 108-degrees is a potential health threat for people, especially seniors.
"With the elderly, it's a different phenomenon. The path of physiology is a little bit differently. It's not that it got so incredibly hot today, and that I was outside today. It's that all summer long. It's been slowly building, and it just overcomes their body's ability to cool, and that's why I'm worried about it this time of the year."
High risk groups such as adults age 55 and older, children under the age of 5 and people with chronic illness, are urged to stay inside air-conditioned areas at the hottest part of the day, between 1 and PM. Dr Persse says we live in a world full of distractions, and that might tax our body's ability to react to the heat.
"The things to safeguard yourself are really pretty simple. You just need to stay hydrated, think ahead about what you're doing and what time of the day you're doing it, give yourself a break, get into some air conditioning. Just think ahead a little bit. It's really not that hard to protect yourself."
The extreme heat is causing air conditioning units to work overtime and long days for repairmen.
It also means hardware stores are doing their best best to keep up with demand. Ernest Rowe is the manager at the Home Depot at Gulfgate.
"Right now, the only air conditioners that I have left are like 8-thousand BTU, and that was like an emergency shipment that we just got in. So, pretty much everything we had, we sold out of due to the heat."
The Houston Health Department says anyone without access to air conditioning can seek shelter during business hours at city multi-service centers, libraries or recreation centers.