--- title: "Acclimatizing New Hires for a Texas Summer Start" description: "A new hire's first week in Texas heat is the riskiest. Use the NIOSH and OSHA rule of 20 percent to build heat tolerance and protect new crew members." url: https://jmarsolutions.multisites.ai/blog/acclimatizing-new-hires-texas-summer publisher: JMAR Solutions phone: +1-214-632-7780 quote: https://jmarsolutions.multisites.ai/contact --- Texas crews # Acclimatizing New Hires for a Texas Summer Start New workers should do 20 percent of a normal heat shift on day one, then add 20 percent each day. OSHA and NIOSH recommend this rule of 20 percent. Experienced workers new to a site start at 50 percent. Almost half of heat-related deaths happen on a worker's first day. Published October 23, 20265 min read ## Why is a new hire’s first week the riskiest? New workers are not used to heat yet. OSHA found that “almost half of heat-related deaths occur on a worker’s first day on the job or a worker’s first day back after an extended absence.” It also found that “over 70 percent of heat-related deaths occur during a worker’s first week.” Texas summers make this a hiring-season issue. A new hire who starts in June meets heat with a body that has not adapted. [Acclimatization](https://jmarsolutions.multisites.ai/glossary/acclimatization) is the fix. ## What changes in the body when a worker acclimatizes? The body gets better at shedding heat. OSHA describes four changes, listed below with the trade-off for an unacclimatized worker. Unacclimatized worker Acclimatized worker Does not sweat efficiently Sweats more, so more evaporative cooling Sweat contains more salt Sweat contains less salt Body temperature and heart rate rise fast Lower body temperature and heart rate at work Blood flow is not set for heat loss More blood flow to the skin to lose heat The change takes days of real work in the heat. A worker who feels fine on day one can still get ill on day two, so the schedule matters. ## What is the rule of 20 percent? It is the standard schedule for brand-new workers. OSHA and NIOSH both recommend it. Day one is 20 percent of the usual heat exposure. Each next day adds 20 percent. Day New worker, share of normal heat exposure Experienced worker new to the site 1 20% 50% 2 40% 60% 3 60% 80% 4 80% 100% 5 100% 100% The new-worker column follows the 20 percent steps. The experienced column comes from the NIOSH schedule: 50, 60, 80, then 100 percent over days one to four. OSHA’s example: for an 8 hour day, a new worker works no more than 1 hour and 40 minutes in the heat on day one, with at least one rest break. For a 10 hour shift, 20 percent is 2 hours. Use the same math for your shift. Our [heat acclimatization schedule guide](https://jmarsolutions.multisites.ai/guides/heat-acclimatization-schedule) has a printable version. ## How do you keep the intensity right? Cut the time, not the effort. OSHA says to “reduce the duration of the work but not the intensity of the work.” Light tasks do not prepare the body for the real job. A new bricklayer should lay bricks in a short block. NIOSH adds that acclimatization “can be maintained for a few days of non-heat exposure.” It also says breaks in air conditioning will not undo it. Use the cooled rest spot. See our [cool-down area setup guide](https://jmarsolutions.multisites.ai/blog/jobsite-cool-down-area-setup). ## What else protects new workers in week one? Watch them closely. OSHA lists these steps for the first one to two weeks. 1. Give shorter heat shifts with more frequent rest breaks. 2. Train new workers on heat illness signs and the value of rest and water. 3. Monitor new workers closely. 4. Use a buddy system. Do not allow new workers to work alone. 5. Let anyone with symptoms stop work, and start first aid. Never leave them alone. New workers often push too hard to prove themselves. OSHA notes they may “ignore heat-related symptoms or continue working despite symptoms.” Tell them on day one that stopping is the right call. ## Do returning workers need a ramp-up too? Yes. OSHA says workers can lose heat tolerance during an extended absence and over winter. Treat these cases like new hires: a return after a week or more, the first warm weeks of spring, and any heat wave. Keep extra protection for at least one week. ## How does hydration support a ramp-up week? New workers sweat hard and may skip drinks. Set a drink schedule at each break. OSHA says crews working two hours or more should have fluids with electrolytes in addition to water. See our [jobsite hydration plan](https://jmarsolutions.multisites.ai/guides/jobsite-hydration-plan) for the full plan, and JMAR’s [hydration programs](https://jmarsolutions.multisites.ai/hydration-programs) for onsite toolbox talks. Rapid Restoration Drops are a dietary supplement. They replace electrolytes lost in sweat and support hydration. Heat stroke is a 911 emergency. ## What does the rule of 20 percent look like for a 10 hour shift? Apply the percentage to your own shift length. For a 10 hour day, 20 percent is 2 hours. The table shows hours in the heat for each day. The numbers are simple math on the OSHA and NIOSH percentages. Round to what your crew can run. Day New worker share Hours in the heat on a 10 hour shift 1 20% 2 hours 2 40% 4 hours 3 60% 6 hours 4 80% 8 hours 5 100% 10 hours The rest of the shift can be in a cooler area or on lighter, non-heat tasks. Include at least one rest break in the heat period. If a worker is not fit or has a health risk, add days. OSHA says that “when in doubt, give workers more days to acclimatize.” ## What can a lead say to a new hire on day one? Use plain words. Try: “Your body needs a week to get used to this heat. Today you work part of the shift here. Drink every break, even if you are not thirsty. Tell me if you feel dizzy, sick, or confused. Stopping is not a problem.” Pair the new hire with a buddy and point out the shade and water. Learn more about the [buddy system](https://jmarsolutions.multisites.ai/glossary/buddy-system) and the [work/rest schedule](https://jmarsolutions.multisites.ai/glossary/work-rest-schedule). ## Who tracks the ramp-up? Assign one lead for each new hire. Use a simple card with the day, hours in the heat, and any symptoms. Keep the card for your records. It shows OSHA that you followed a schedule. ## Next step Starting new hires this spring? [Book a 15-minute demo](https://calendly.com/jen-jmarsolutions/15-min-meeting) to get a first-week heat talk for your leads, or ask for a [free sample](https://jmarsolutions.multisites.ai/free-sample). ## Frequently asked questions ### How long does it take to acclimatize to heat? NIOSH says to increase time in hot conditions gradually over 7 to 14 days. Workers who are not physically fit need more time. OSHA says to keep extra protections for one to two weeks for new workers. ### What is the rule of 20 percent? New workers do no more than 20 percent of the usual heat exposure on day one. Then they add no more than 20 percent each day. OSHA and NIOSH both recommend it. For an 8 hour day, day one is 1 hour and 40 minutes in the heat. ### Do returning workers need to acclimatize too? Yes. OSHA says workers can lose heat tolerance during an extended absence or over winter. Existing workers are at higher risk when they return after a week or more away, when spring heat starts, and on any day much hotter than the days before. ## Terms on this page - [Work/rest schedule](https://jmarsolutions.multisites.ai/glossary/work-rest-schedule) - [Acclimatization](https://jmarsolutions.multisites.ai/glossary/acclimatization) - [Buddy system](https://jmarsolutions.multisites.ai/glossary/buddy-system) - [Heat stroke](https://jmarsolutions.multisites.ai/glossary/heat-stroke) - [Hydration](https://jmarsolutions.multisites.ai/glossary/hydration) - [NIOSH](https://jmarsolutions.multisites.ai/glossary/niosh) ## Sources 1. [OSHA: Heat, Protecting New Workers](https://www.osha.gov/heat-exposure/protecting-new-workers) 2. [OSHA: Heat, Protecting New Workers](https://www.osha.gov/heat-exposure/protecting-new-workers) 3. [OSHA: Heat, Protecting New Workers](https://www.osha.gov/heat-exposure/protecting-new-workers) 4. [CDC NIOSH: Heat Stress, Workplace Recommendations](https://www.cdc.gov/niosh/heat-stress/recommendations/index.html) 5. [CDC NIOSH: Heat Stress, Workplace Recommendations](https://www.cdc.gov/niosh/heat-stress/recommendations/index.html) 6. [OSHA: Heat, Water. Rest. Shade.](https://www.osha.gov/heat-exposure/water-rest-shade) 7. [OSHA: Heat, Protecting New Workers](https://www.osha.gov/heat-exposure/protecting-new-workers) Checked against the sources above on October 23, 2026. Rules and guidance change, so check the linked page before you act. This page is general information, not legal or medical advice. ## Keep reading - [A heat acclimatization schedule for new and returning workersNIOSH says to build heat tolerance over 7 to 14 days. New workers do no more than 20% of the usual time in the heat on day 1, then add no more than 20% each day. Experienced workers can do 50%, 60%, 80%, then 100% on days 1 through 4. Cut the time, not the work intensity.](https://jmarsolutions.multisites.ai/guides/heat-acclimatization-schedule) - [A jobsite hydration plan that crews followNIOSH says workers doing moderate activity in the heat for under 2 hours should drink 1 cup (8 oz) of water every 15 to 20 minutes. If sweating lasts several hours, NIOSH says to drink sports drinks with balanced electrolytes. Fluid intake generally should not exceed 6 cups per hour.](https://jmarsolutions.multisites.ai/guides/jobsite-hydration-plan) - [How to Set Up a Jobsite Cool-Down Area (Water, Rest, Shade)A cool-down area gives crews water, rest, and shade in one place near the work. OSHA says water should be cool and easy to reach, breaks should grow longer as heat stress rises, and shade can be a tent, a building, or an air-conditioned vehicle. Set it up before the shift starts.](https://jmarsolutions.multisites.ai/blog/jobsite-cool-down-area-setup) - [Heat illness: signs, first aid and when to call 911Heat stroke is an emergency. Call 911, stay with the worker, move them to shade and cool them fast. NIOSH says body temperature can reach 106°F within 10 to 15 minutes. Heat exhaustion needs medical evaluation. Heat cramps, heat rash, fainting and rhabdo each have their own signs and steps. Know them before the shift.](https://jmarsolutions.multisites.ai/heat-illness) - [Heat stress prevention for high-risk crewsHeat stress prevention starts with water, rest and shade, then adds acclimatization for new workers, supervisor training and a written plan. NIOSH says to give workers cool water near the work area and to build up heat exposure over 7 to 14 days. Electrolytes support hydration when a crew sweats for hours.](https://jmarsolutions.multisites.ai/heat-stress-prevention) - [Build a heat stress program in 8 stepsA heat stress program has eight parts: name a daily lead, measure heat on site, set advisory-day triggers, give water, rest and shade, acclimatize workers, train everyone, plan first aid and 911, then review. OSHA says employers should write the plan down. This follows OSHA and NIOSH guidance, not a final federal rule.](https://jmarsolutions.multisites.ai/guides/heat-stress-program-for-employers) ![Ironworkers silhouetted on a steel frame against a hot orange sunset](https://jmarsolutions.multisites.ai/_astro/sunset-steel.IhAMDca0_6wk53.webp) ## See it on your crew in 15 minutes Jennifer walks your safety team through the drops, the protocol and the numbers on a short live call. [Book a 15-minute demo](https://calendly.com/jen-jmarsolutions/15-min-meeting)