What Is a Trigger Depth in Commercial Snow Removal?

A trigger depth is the contractual threshold that starts winter service. SIMA's industry glossary defines it as the agreed-upon measurable amount of accumulated snow or ice wherein snow and ice management services are dispatched. The contract also names the measurement location and the party responsible for measuring, which removes disputes about when the threshold was reached.

The trigger is one form of a service initiator. Other initiators include weather forecasts, temperature-and-moisture conditions, and written client requests. The trigger answers when work starts; a separate contract term, the level of service, answers what the finished surface looks like and by what time.

Common commercial trigger depths are 1 inch, 2 inches, and 3 inches. Facility management guidance tiers them by surface priority. Building entrances, emergency access, and accessible ramps carry a 1-inch trigger. Main drive lanes, parking aisles, and primary walkways carry 2 inches. Remote parking areas and secondary walkways carry 3 to 4 inches.

Property type sets the threshold. The table pairs each with its typical service level.

Zero tolerance is a service level with no minimum accumulation: any measurable snow, freezing drizzle, or ice condition starts service. In practice, zero tolerance work begins with pretreatment before the storm and continues through the event, with crews returning as conditions change. SIMA classifies zero tolerance as a low-tolerance descriptor rather than a complete level of service, since completion times and surface expectations still get defined separately.

The working goal on a zero tolerance site is bare and wet pavement. Industry guidance is blunt about the ceiling. A slip-free surface at every moment of every storm is not an achievable condition, and a contractor promising one is overpromising. What zero tolerance delivers is active management, including around-the-clock deployment through services such as Emergency Plowing and Deicing when storms land overnight, on weekends, or on holidays.

A weather trigger dispatches crews on atmospheric conditions instead of measured accumulation, and that difference decides winter safety in this region. NOAA data for the Seattle-Tacoma area recorded 146 days of snowfall from 1990 to 2003, and 131 of those days produced under 1 inch. A property on a 1-inch depth trigger received zero service on roughly 9 out of 10 regional snowfall days across that period, while pavement still glazed.

Ice, refreeze, and black ice are the dominant Puget Sound lowland hazards, and all 3 form at zero measurable depth. The regional answer is a condition trigger: when the temperature reaches 32°F with moisture in the air, crews roll before accumulation exists. That model treats freezing drizzle on a Tuesday night with the same seriousness as a plowable storm, because injury claims start on glazed walkways, not deep drifts. Ice response runs through Commercial Deicing, applied when conditions call for it rather than on a calendar.

Site monitoring activates a trigger by reading each property against professional meteorological forecasting through the whole winter. Regional forecasts miss local variation. The Puget Sound Convergence Zone forms when air flowing around the Olympic Mountains collides over the Sound, dropping narrow, intense precipitation bands. The zone most often sets up across central and south Snohomish County and reaches as far south as northern Pierce County. That is why a Kent warehouse can sit under ice while a Tacoma medical campus stays dry.

Per-site monitoring pairs each property's trigger with its own conditions, and measured readings size the product application to what the site actually needs. That is the operating model behind Commercial Snow & Ice Management: each site read separately, each trigger fired on its own conditions.