Data Center Cooling Vest: Build Crews and Hot Aisle Work

Who is actually in the heat

Two crews, two completely different heat problems.

Most heat-safety thinking about data centers stops at PUE and airflow, which is about the equipment. The people problem splits cleanly in two, and the gear that fits one does not automatically fit the other.

Phase one

The build

Before there is a roof there is a slab, and it is usually in a hot region on cheap open land near power. This is ordinary construction heat, made worse by an unusually unforgiving schedule.

Steel erection and roof deck work in full sun, on dark surfaces
Electrical rough-in, busway and switchgear installs at pace
Mechanical trades in an enclosed shell before the cooling plant runs
Commissioning crews working against a live equipment delivery date

Phase two

The live facility

Containment works by keeping hot exhaust separated and concentrated. That is excellent for the servers. It means anyone on the hot side is standing in the collected waste heat of a rack line.

Cable pulls and drive swaps on the hot side of containment
Electricians and techs in rooms with no meaningful air movement at body level
Generator and UPS rooms, which are their own heat problem
Anything that goes wrong at 2am, when the response is a person, not a script

Steel roof framing and cladding on a data center under construction, with lifts working along the wall — A data hall shell before the cooling plant exists. The trades inside are working in an enclosed box in summer.

The schedule is the reason this bites harder here. A data center build is paced by when the equipment lands, not by the forecast. When heat slows a crew or forces a stand-down, the slip lands on a critical path that has a contracted go-live at the end of it.

Which is the honest commercial argument for cooling gear on these jobs: it is not a wellness benefit, it is schedule protection. The ROI calculator runs the numbers on your own crew size and shift length.

Data center construction

The hottest segment in construction is being built by an industry that cannot staff it.

This is where most of our units go, and the reason is not really the heat. It is the arithmetic underneath the heat. Data center construction is the one segment contractors are genuinely bullish on, and it is being delivered by a workforce that is harder to hire into than at any point in the last three years.

65%

Of contractors expect data center work to grow

Against 8% expecting it to shrink, a net +57 and the strongest reading of any segment. AGC, Dampened Expectations: The 2026 Construction Hiring and Business Outlook.

82%

Of firms struggle to fill hourly craft positions

A higher proportion than at any point in the past three years. Same survey, 951 respondents, fielded Nov to Dec 2025.

57%

Name worker supply as a top concern for 2026

While 63% still expect to add headcount. The demand is there; the people are the constraint.

36%

Of US occupational heat deaths are in construction

1992 to 2016, 285 deaths, while construction was about 6% of the workforce. CDC/NIOSH, 21 May 2020.

Why heat costs more here

Turnover is the expensive part.

On a normal job, a worker who walks off in August is a scheduling problem. On a data center build, in a trade where four out of five firms cannot fill craft openings, that worker may simply not be replaced this season.

The electricians, pipefitters and controls techs on these jobs are the exact crafts the survey says are hardest to hire
Heat is a working condition people quit over, and the ones with the most options leave first
A crew that loses two people in a heat wave does not get two people back, it gets overtime and a slipped date
Retention is worth more when replacement is hard, which is the whole argument for spending on conditions

What the build actually is

Heavy construction, on a chip delivery date.

Before the building can cool anything, it is a slab on open ground in a hot region near cheap power. Every trade on it is working in ordinary construction heat against an unusually unforgiving schedule.

Steel erection and roof deck work in full sun, on dark surfaces
Electrical rough-in, busway and switchgear at pace
Mechanical trades inside an enclosed shell before the cooling plant runs
Commissioning against a live equipment delivery date that will not move for weather

The compliance floor is the same as any other site: OSHA's Heat National Emphasis Program covers construction specialty trades and triggers a heat priority day at a forecast heat index of 80°F, and several states with heavy data center build-out enforce their own rules. Detail on the construction page and in the heat safety laws directory.

The number everyone quotes wrong

How hot does a hot aisle actually get?

The familiar data center temperatures are inlet temperatures: the air going into the rack. ASHRAE's thermal guidelines put the recommended server inlet range at 64.4 to 80.6°F, and the allowable range runs to 89.6°F for Class A1 equipment and as high as 113°F for Class A4. The hot aisle is what comes back out the other side, after that air has crossed the servers.

41°FServer inlet temperature120°F

Every marker on that bar is an inlet spec. None of them describe the aisle a person is standing in. The exhaust side sits above the inlet by whatever temperature rise the equipment adds, which is why a room that is comfortably within spec for the hardware can still be a genuine heat-stress environment for the crew working the back of the rack.

Source: ASHRAE TC 9.9, Thermal Guidelines for Data Processing Environments, 5th edition, 2021. Clema does not publish a hot-aisle temperature figure because it depends entirely on the equipment, the containment design and the load, and any single number would be marketing rather than measurement. Measure your own aisles.

The controls, in order

How do you keep people cool in a hot data center?

In the order a safety officer should work through them, because the cheap fixes come first and the gear comes last. The complication specific to this building is that the two moves you would make anywhere else are both unavailable: you cannot prop a door and you cannot point a fan at someone.

Start here

Fix the airflow before you buy anything.

Close the containment. Missing blanking panels and unsealed floor cutouts let hot exhaust recirculate into the cold aisle, which makes both aisles worse and is free to fix.
Work the cold side where the task allows it. A surprising share of hot-aisle time is habit rather than necessity.
Rotate people out of the aisle on a clock, not on how they feel. By the time someone notices, they are already behind.
Give them somewhere genuinely cool to go. The NOC is not a cool-down area if it is warm. Cal/OSHA's indoor rule is explicit that the cool-down space has to actually be cool.
Water within reach of the work, not at the other end of the hall past two badge readers.

Why the usual fixes are off the table

You cannot open a door or add a fan.

A door is part of the airflow design. Propping containment open to cool a person degrades the cooling for the whole rack line, and the facility team will close it.
A fan moves the wrong air. OSHA's own guidance says air movement helps only while the air is cooler than skin, "usually less than 95 degrees F dry bulb". In a hot aisle it is not, so a fan is moving hot air across a hot person.
Spot coolers reject heat into the room they are standing in, and into the building's cooling load.
Which is why the last rung is cooling worn on the person, sized so it does not need water, ice or a freezer.

This ladder is the same hierarchy every heat rule uses: engineering controls, then administrative controls, then personal protective equipment. Personal cooling is the bottom rung, not a substitute for the rungs above it. See the Cal/OSHA indoor rule for how that hierarchy is written into law, and how to stay cool on a job site for the outdoor version.

Recognise it early

What do you do when a worker overheats?

An overheated worker in a data hall is a harder problem than an overheated worker on a roof, because the nearest genuinely cool place may be several doors away and the room they are standing in is designed to hold heat, not shed it. Know which of these two you are looking at before you decide how fast to move.

	Heat exhaustion	Heat stroke
What you see	Fatigue, irritability, thirst, nausea or vomiting, dizziness, heavy sweating, elevated temperature or fast heart rate	Confusion, slurred speech, unconsciousness, seizures, heavy or absent sweating, very high temperature, fast heart rate
What you do	Move them somewhere cooler, take off heavy clothing, cool actively with ice or cold wet towels, keep them monitored	Call 911 immediately and cool with ice or cold water until help arrives. Do not wait to see if it improves
In a data hall	The cold aisle is cooler than the hot aisle but it is not a cool-down area. Get them out of the room	Send someone to meet the ambulance at the gate. Secure sites cost minutes that a heat stroke does not have

Signs and first aid as published by OSHA, whose own summary is the one worth memorising: when in doubt, cool the worker and call 911. Confusion or slurred speech is the line between the two columns. Nothing on this page is medical advice, and it does not replace your site's emergency response plan or a trained first aider.

The numbers behind it

Fifty billion a year, built in the hottest places.

Data centers went from a line item buried inside office construction to their own category, and then past office construction entirely. The sites follow cheap land and cheap power, which in practice means Texas, Arizona, Georgia and Virginia rather than anywhere temperate.

$50.7B

Annualized US data center construction

April 2026, seasonally adjusted annual rate, up about 28% year over year. US Census Bureau, Value of Construction Put in Place.

113°F

Top of the ASHRAE A4 allowable inlet range

Class A4 equipment, allowable server inlet. ASHRAE TC 9.9, 5th ed., 2021. Inlet, not aisle.

Construction workers killed by environmental heat in 2024

Of 48 across all US industries. Half the national total, in one sector. BLS Census of Fatal Occupational Injuries, 2024.

80°F

Heat index that triggers an OSHA heat priority day

National Emphasis Program CPL 03-00-024, renewed 10 April 2026 for up to five years across 55 target industries.

The category problem

Most cooling gear brings water into an electrical room.

This is the constraint that makes data centers different from every other hot worksite. On a roof, meltwater is a nuisance. Beside energized busway and switchgear it is a conversation with the facility manager that ends with the vest going back in the truck.

Type	Why it struggles in a data hall	Runtime
Ice vest	Melts. Produces condensation and meltwater, and needs a freezer the building does not have	1–2 hr
Phase-change (PCM)	Same freezer problem, plus hours of reset time between uses	2–3 hr
Evaporative	Wet by design. Has to be re-soaked to keep working, and needs dry moving air to do anything	Varies
Fan vest	Moves ambient air across the body, which does nothing once that air is hotter than skin	Battery-limited
Solid-state (Clema)	Runs dry. No ice, no meltwater, no re-soaking. Makes cold electrically instead of carrying a store of it	8–12 hr

On fan vests specifically, OSHA's own heat guidance says air movement "is generally only effective as long as the air temperature is less than the worker's skin temperature (usually less than 95 degrees F dry bulb)". A hot aisle is precisely the case where that stops being true. Full teardown in the cooling vest comparison.

Where Clema fits, and where it does not.

Sub-3-lb, worn under a hi-vis vest against a thin base layer, works with a fall-arrest harness, and runs 8 to 12 hours on one battery swap. Nothing to freeze, nothing to soak, nothing to drip.

The limit, stated plainly: Clema is not rated for wear under flame-resistant or arc-rated garments. If the task is arc-flash PPE work, this is not the product for that task, and any vendor telling you otherwise is worth a second question.

An industrial worker wearing a Clema cooling vest under an open hi-vis vest, with the battery at the waist — Clema worn under a hi-vis vest at an industrial site. The vest goes against a base layer, hi-vis over the top.

The regulatory position

What actually applies to a data center job.

There is still no federal heat standard in force. The proposed rule has a supplemental notice scheduled for December 2026 and final action targeted for October 2027, so anyone selling you compliance with a federal heat rule today is selling you something that does not exist yet.

What applies	Where it bites on a data center build
General Duty Clause	The federal route for citing heat today. It has no temperature trigger, which cuts both ways
Heat NEP, CPL 03-00-024	Renewed 10 April 2026 for up to five years, 55 target industries including construction specialty trades. Heat priority day at a forecast heat index of 80°F
State rules	California, Washington, Oregon, Maryland, Nevada, Colorado and Minnesota enforce their own. California's indoor rule (section 3396) reaches commissioned facilities, not just the build

Cooling gear is supplemental PPE under every one of these hierarchies. It does not replace water, shade, rest or a written plan, and we will not tell you it does. It extends the safe productive time you get between the breaks the rule already requires. State by state detail is in the heat safety laws directory, and the California indoor rule is broken down on the Cal/OSHA page.

If you want units on a job

What happens after you apply.

The first production batch is 500 units for summer 2026, and crews with documented heat exposure get priority. Here is the whole process, so you know what you are signing up for.

You apply

Crew size, site, shift length and what the heat exposure actually looks like. Two minutes, and the phone number is optional.

We reply in 5 business days

A real answer either way, including a no. If the fit is wrong for your tasks we will say so rather than take the slot.

Sizing and allocation

Send us the height and weight range across the crew and we work out the split with you before anything ships.

Apply for early access Talk to the team first

FAQ

Straight answers.

How do you keep workers cool in a hot data center?

Work the controls in order, because the cheap ones come first. Close the containment: missing blanking panels and unsealed floor cutouts let hot exhaust recirculate, which makes both aisles worse and costs nothing to fix. Do the task from the cold side where it is possible. Rotate people out of the hot aisle on a clock rather than on how they feel. Give them a genuinely cool space to go to, which a warm NOC is not. Keep water within reach of the work. Personal cooling is the last rung, not the first, and in a data hall it has to run dry because ice and evaporative gear bring water near energized equipment.

Why can't you just use fans to cool workers in a data hall?

Two reasons. OSHA's own guidance says air movement helps only while the air is cooler than skin, usually below 95 degrees F dry bulb, and a hot aisle is above that, so a fan is moving hot air across a hot person. The second reason is specific to this building: a fan or a propped containment door disrupts the airflow design, degrades cooling for the whole rack line, and the facility team will shut it down. Spot coolers have the same problem in reverse, because they reject their heat into the room and into the building's cooling load.

What do you do when a worker overheats in a data center?

Work out which of two things you are looking at. Heat exhaustion shows as fatigue, irritability, thirst, nausea, dizziness, heavy sweating and a raised temperature or fast heart rate: move them somewhere cooler, remove heavy clothing, cool actively with ice or cold wet towels, and keep them monitored. Heat stroke shows as confusion, slurred speech, unconsciousness, seizures, heavy or absent sweating and a very high temperature: call 911 immediately and cool with ice or cold water until help arrives. OSHA's own summary is the one to memorise, which is that when in doubt you cool the worker and call 911. In a data hall, remember the cold aisle is not a cool-down area and a secure site can cost an ambulance several minutes at the gate.

How does heat affect turnover on a data center construction site?

It costs more here than on a normal job because the worker is harder to replace. AGC's 2026 Construction Hiring and Business Outlook found 82% of firms having a hard time filling hourly craft positions, a higher proportion than at any point in the previous three years, and 57% naming insufficient supply of workers or subcontractors as a top concern. The same survey found data center construction the most bullish segment of all, with 65% of contractors expecting the market to grow against 8% expecting it to shrink. So the demand is concentrated on exactly the trades that are hardest to hire. Heat is a working condition people quit over, and the people with the most options leave first, which means a crew that loses two electricians in a heat wave does not get two back. It gets overtime and a slipped date. Retention is worth more when replacement is hard.

What cooling do data center construction crews need?

Before the building can cool itself, a data center site is ordinary heavy construction in a hot region: steel erection and roof deck work in full sun, electrical rough-in and busway at pace, and mechanical trades inside an enclosed shell with no cooling plant running yet. The difference is the schedule, which is paced by equipment delivery dates rather than by weather, so heat-driven stand-downs land directly on a critical path with a contracted go-live at the end of it. Crews need the same hierarchy as any site, water, shade and rest first, plus cooling that lasts a full shift rather than the hour or two ice and phase-change gear manage.

How hot does a data center hot aisle get?

Hotter than the numbers most people quote, because the familiar figures are inlet temperatures. ASHRAE's thermal guidelines set a recommended server inlet range of 64.4 to 80.6°F, with allowable inlet ranges running to 89.6°F for Class A1 equipment and as high as 113°F for Class A4. That is the air going into the rack. The hot aisle is what comes back out after it has passed over the servers, so it sits above the inlet figure by the temperature rise across the equipment. A crew pulling cable or swapping drives in that aisle is standing in the exhaust.

Is a data center air conditioned for the workers?

No. A data hall is precision climate-controlled for the equipment, and the design intent is to keep cold air at the server inlets and move waste heat away from them efficiently. Containment does that by keeping the hot air separated and concentrated, which is good for the machines and worse for anyone standing on the hot side of the containment. The building is a cooling system that is not pointed at people.

Why do ice and evaporative cooling vests fail in a data hall?

Because both of them bring water into a live electrical room. Ice vests melt and produce condensation and meltwater. Evaporative vests have to be soaked to work and are wet by design. Neither is something a facility team wants near energized racks, busway or switchgear, and both also run out fast: ice fades in about one to two hours and phase-change packs need a freezer that a data hall does not have. Solid-state cooling runs dry, which is the reason it fits this environment.

Does OSHA's heat program apply to data center construction?

Yes. OSHA renewed its National Emphasis Program on heat on 10 April 2026 for up to five years, covering 55 target industries including construction specialty trades. There is still no federal heat standard in force, so heat is cited under the General Duty Clause, but a heat priority day is triggered by a forecast heat index of 80°F or above and inspections follow. Several states with heavy data center build-out, including California, also enforce their own heat rules.

What cooling vest works for electricians in a data center?

One that runs dry, fits under a hi-vis vest and lasts the full shift rather than an hour. Clema is a sub-3-lb solid-state system that makes cold electrically instead of carrying a store of it, so there is no ice, no meltwater and no re-soaking, and it runs 8 to 12 hours on one battery swap. Note the honest limit: Clema is not rated for use under flame-resistant or arc-rated garments, so it is not the answer for arc-flash PPE tasks.

How big is data center construction right now?

US private data center construction was running at a seasonally adjusted annual rate of about $50.7 billion in April 2026, up roughly 28% year over year, and it now exceeds conventional office construction. The Census Bureau only began breaking data centers out as their own line in mid-2024. That scale matters for heat because these are large-footprint sites, often on open ground in hot regions, built to schedules set by equipment delivery dates rather than by weather.

Cooling for Data Center Crews: The Room Is Cooled for the Machines