Nearly one in five Massachusetts workers are outdoors. A new tool maps who.

As summer heat intensifies, the workers most exposed to it aren't evenly distributed across the population — they cluster heavily in specific industries, genders, and racial groups. A study published this month in the Journal of Occupational & Environmental Medicine builds a tool specifically designed to identify who those workers are, using Massachusetts as its test case [s1].

What the researchers built

Rather than surveying workers directly about their heat exposure, the researchers developed what they call an Outdoor Occupational Exposure Matrix — a system that assigns an outdoor-or-indoor exposure level to each occupation category [s1]. They then applied that matrix to American Community Survey data from 2018 to 2022 to estimate how many Massachusetts workers actually work outdoors, and characterize who they are [s1].

Who works outdoors, by the numbers

The analysis estimated that 17.5% of Massachusetts workers — nearly 641,000 people — work outdoors [s1]. That exposure was heavily concentrated by industry: 80.2% of construction workers were classified as working outdoors, far above the statewide average [s1]. The gap by sex was substantial too: 28.1% of male workers worked outdoors compared with 6.4% of female workers [s1]. By race and ethnicity, the highest outdoor-work percentage was among American Indian/Alaska Native, non-Hispanic/non-Latino workers, at 29.2% [s1].

Why a matrix like this matters

Climate-related heat research has historically had to choose between two imperfect options: broad population-level heat mortality data that doesn't distinguish who was actually exposed to heat while working, or narrow, resource-intensive surveys of specific occupational groups that don't scale to a full workforce. An occupation-based exposure matrix offers a middle path — it lets researchers estimate outdoor exposure across an entire state's workforce using existing labor-force survey data, without having to survey every worker directly about their working conditions [s1].

What the researchers say it's for

The study's authors describe the matrix as a resource intended for climate-related health research and practice broadly [s1], with a specific practical aim: understanding the number and demographic characteristics of workers likely to be exposed to outdoor heat can inform planning and the equitable implementation of prevention efforts [s1] — meaning heat-safety programs, workplace protections, and public health outreach could, in principle, be targeted using this kind of occupational breakdown rather than applied uniformly across a workforce where actual heat exposure varies enormously by job.

What the data does and doesn't capture

This is a Massachusetts-specific analysis built on national labor-force survey categories, and the researchers themselves describe it as a demonstration of the matrix methodology using Massachusetts as a case study — the specific percentages reported here describe that state's workforce during 2018–2022, not a national estimate, though the underlying method could in principle be applied to other states' workforce data [s1]. The matrix also measures exposure at the level of an occupation category rather than tracking any individual worker's actual heat exposure on a given day, so it identifies who is more likely to face outdoor heat as a structural feature of their job, not who has already experienced a specific heat-related illness [s1].

Sources

• Identifying workers at risk of exposure to climate-related health hazards using the Outdoor Occupational Exposure Matrix: A characterization of the Massachusetts workforce — Journal of Occupational & Environmental Medicine, 2026-06-30