Block Insulation — Asbestos Exposure Crosswalk

What This Equipment Is

Block insulation is rigid, rectangular thermal insulation in slab form — typically 6 × 12 to 12 × 36 inches and 1 to 4 inches thick. Insulators fit blocks to the curved or flat surfaces of large equipment that pipe-section insulation can’t wrap: boiler shells, steam drums, turbine casings, pressure vessels, heat exchangers, breechings, ducts, and tanks.

For most of the twentieth century, the standard block insulations were asbestos-bearing:

  • Calcium silicate block — workhorse high-temperature block
  • 85% Magnesia block — earlier era, replaced by calcium silicate in the 1950s–60s
  • Asbestos-cement block — extreme high-temperature service
  • Fiberglass-asbestos block — transitional blends

Why Block Insulation Work Was a High-Exposure Activity

Same two pathways as pipe insulation: installation and removal.

Installation involved cutting blocks to fit with hand saws or knives (cut ends released chrysotile dust at close range), troweling on insulating cement to seat the block, wiring the block in place, and finishing with a cement coat or canvas jacket.

Removal was even dustier. Thermally cycled block insulation becomes brittle, friable, and crumbles when struck or pried. Stripping it off a boiler shell or turbine casing — particularly inside the confined space of a boiler house during an outage — generated dense airborne fiber concentrations sustained over many shifts.

Manufacturers Named in Block-Insulation Litigation

  • Johns-Manville — calcium silicate, magnesia, asbestos-cement block
  • Owens-Corning / Fibreboard — Kaylo block
  • Eagle-Picher — block insulation
  • Armstrong World Industries — calcium silicate block
  • Pittsburgh Corning — Unibestos block
  • Combustion Engineering — insulation products
  • W.R. Grace — fireproofing and insulating products

Documented Product References

Images sourced from publicly available product-identification reference materials. Inclusion does not constitute a finding of liability against any company.

Trust Funds That May Apply

  • Manville Personal Injury Settlement Trust
  • Owens-Corning / Fibreboard Asbestos PI Trust
  • Eagle-Picher Industries PI Settlement Trust
  • Pittsburgh Corning Corporation Asbestos PI Trust
  • Armstrong World Industries Asbestos PI Settlement Trust
  • Combustion Engineering 524(g) Asbestos PI Trust
  • W.R. Grace Asbestos PI Trust

Trades Most Exposed at Block Insulation

Insulators (Heat & Frost Insulators), boilermakers and millwrights working alongside insulators during outages, laborers doing tear-out, maintenance mechanics.

Jobsites in the Network Documenting Heavy Block-Insulation Use

The Trade That Installed These Products

Heat & Frost Insulators were the trade dispatched to install, remove, and re-install these materials at virtually every industrial, institutional, and military facility built between 1920 and 1980. The trade has one of the most-documented mesothelioma rates of any occupation in U.S. federal occupational-health research.

For the comprehensive Heat & Frost Insulators trade reference — including Local union jurisdictions across the country, the full asbestos product catalog the trade handled, workplace categories, applicable bankruptcy trust funds, and state-specific filing deadlines — see the partner site:

insulatorsmesothelioma.com — Heat & Frost Insulators trade reference

Compiled from publicly filed asbestos litigation, EPA / state-DNR records, and industry-publication histories. Product and company references reflect what has been alleged or documented in publicly filed litigation. This page does not constitute a finding of liability against any company. Not legal advice; consult a licensed attorney about your specific situation.