Mizzou GR / Steelplant Castable B / AP Green Castable Mix

Product Description

Mizzou GR, Steelplant Castable B, and AP Green Castable Mix are trade names for a family of high-temperature refractory castable products manufactured by A.P. Green Industries, Inc. between approximately 1948 and 1978. These products were engineered for use in industrial furnaces, kilns, boilers, and other extreme-heat applications where conventional masonry brick or mortar could not withstand sustained elevated temperatures or thermal cycling.

A.P. Green Industries was one of the most prominent refractory manufacturers in North America throughout the mid-twentieth century, supplying products to steel mills, foundries, power generation facilities, chemical plants, and heavy manufacturing operations. The castable mixes under the Mizzou GR and Steelplant Castable B trade names were specifically formulated for steel industry applications, where ladles, tundishes, soaking pits, and furnace linings demanded materials that could endure continuous contact with molten metal and slag. AP Green Castable Mix served as a more general-purpose refractory product used across a wider range of industrial settings.

These products were typically supplied in dry powder or aggregate form and mixed with water on-site before being poured, troweled, or gunned into place. Once cured and fired, the hardened castable formed a dense, heat-resistant lining that required periodic repair, patching, and eventual removal as industrial equipment aged or changed service conditions.

Asbestos Content

A.P. Green Industries incorporated chrysotile asbestos into Mizzou GR, Steelplant Castable B, and AP Green Castable Mix during their production period of 1948 through 1978. Chrysotile, also known as white asbestos, was the predominant commercial asbestos fiber type used in the United States during the postwar industrial expansion. Its fine, curly fiber structure made it well-suited for blending into refractory matrices, where it contributed to tensile reinforcement, thermal resistance, and resistance to cracking under heat stress.

The inclusion of chrysotile asbestos in these castable products was consistent with standard refractory industry practice during this period. Asbestos fibers were valued for their ability to reduce shrinkage cracking during initial cure and firing cycles, improve the handling characteristics of wet castable mixes, and enhance the durability of finished linings under mechanical and thermal shock. Documentation submitted in connection with the A.P. Green Industries Asbestos Settlement Trust confirms that these product lines contained asbestos and that workers who handled or disturbed them faced exposure risk.

The Hazardous Air Pollutants provisions under the Clean Air Act and subsequent EPA rulemaking under AHERA have since identified chrysotile asbestos as a regulated substance. OSHA standards at 29 CFR 1910.1001 and 29 CFR 1926.1101 establish permissible exposure limits and required controls for asbestos-containing materials in both general industry and construction settings.

How Workers Were Exposed

Industrial workers in steel mills, foundries, power plants, and other heavy manufacturing facilities faced the primary occupational exposures associated with Mizzou GR, Steelplant Castable B, and AP Green Castable Mix. Exposure pathways were numerous and often overlapping, depending on a worker’s specific trade and the stage of the product’s service life.

Mixing and Installation: Workers who mixed dry castable material with water on-site generated airborne dust during the pouring, blending, and agitation process. The dry powder formulation meant that any disturbance of unset material released respirable chrysotile fibers into the breathing zone. Finishers, trowelers, and laborers who applied wet castable to furnace walls, ladle linings, and kiln interiors worked in close proximity to freshly mixed material throughout installation.

Gunning Operations: Many industrial applications called for refractory material to be applied pneumatically through gunning equipment. This process, which projected a stream of mixed castable at high velocity onto a substrate, produced dense clouds of airborne particulate. Workers operating gunning equipment and those nearby were exposed to sustained concentrations of dust containing chrysotile fibers.

Repair and Patching: Furnace and kiln linings required regular maintenance. Workers assigned to patch or resurface worn areas of existing castable linings broke into, chipped, and ground away hardened material, releasing previously bound asbestos fibers. Repair work often occurred in confined spaces such as furnace interiors, where natural ventilation was limited or absent.

Demolition and Relining: At the end of a lining’s service life, crews demolished the spent refractory material using pneumatic hammers, chisels, and hand tools. This process generated heavy concentrations of airborne dust. Workers in adjacent trades—pipefitters, millwrights, boilermakers, and ironworkers—who were present during demolition or relining activities also faced secondary exposure through shared work environments.

Ventilation controls, respiratory protection, and wet methods were not consistently implemented in industrial settings during the decades these products were in service. The lack of hazard communication regarding the asbestos content of refractory castables left workers without adequate information to protect themselves.