The Insurance Services Office (ISO) boiler and machinery coverage form (BM 00 25 06 95) is designed to dovetail with ISO's building and personal property coverage form (CP 00 10) and its causes of loss forms (CP 10 10 06 95 basic causes of loss form; CP 10 20 06 95, broad causes of loss form; and CP 10 30 06 95, special causes of loss form). The property causes of loss forms exclude coverage provided by the boiler and machinery form and they cover perils excluded by the boiler and machinery form. For example, the property forms exclude explosion of steam boilers, which are covered by the boiler and machinery form. On the other hand, the property forms cover the explosion of gasses in the furnace of a boiler, an excluded peril on the boiler and machinery form.

The Peril of Explosion

The description of the named peril explosion in the basic and broad property causes of loss forms and the exclusion of steam boiler explosion in the same forms set forth a distinction that can be drawn between the commercial property and boiler and machinery forms.

The named peril property forms define the insured explosion peril as, “Explosion, including the explosion of gasses or fuel within the furnace of any fired vessel or within the flues or passages through which the gasses of combustion pass. . . .” So far, any explosion, and specifically gas combustion explosions, are covered perils in the commercial property forms.

The property causes of loss forms then exclude the “explosion of steam boilers, steam pipes, steam engines or steam turbines . . . . But if loss or damage by fire or combustion explosion results we will pay for that resulting loss or damage.” To bring it in line with the named peril forms, the special causes of loss form adds, “We will also pay for loss or damage caused by or resulting from the explosion of gasses or fuel within the furnace of any fired vessel or within the flues or passages through which the gasses of combustion pass.”

The distinction is that the property form covers explosion due to combustion of gasses (among other types of explosion) while the boiler and machinery policy is designed to cover only explosion resulting from excessive pressure in steam boilers and other vessels.

This distinction between combustion explosion and excessive pressure explosion is further supported in the boiler and machinery policy, which excludes all types of explosion except the “explosion of any steam boiler, electric steam generator, steam piping, steam turbine, steam engine, gas turbine, or moving or rotating machinery caused by centrifugal force or mechanical breakdown.” The boiler and machinery form reinforces the distinction also by excluding loss from “Explosion of gas or unconsumed fuel within the furnace of any boiler or fired vessel or within the passages from that furnace to the atmosphere.” The boiler and machinery and commercial property forms make it clear that boiler and machinery forms cover only excessive pressure explosions, while commercial property forms cover all explosions except excessive pressure explosions.