Breakthrough Indicator Stickers for Wolverine Brand odor filters from Simple Solutions Distributing indicate when the carbon is saturated and will require replacement, keeping the technician ahead of odor complaints. They change from green to brown to black. The change to brown occurs when 1 ppm of hydrogen sulfide is detected at the outlet of the filter. The 148SS model is specifically made for manhole filters, while the 153WP can be applied to any Wolverine Brand odor filter, with the exception of the WVI inline filter and MNHL manhole filter. 866/667-8465; www.industrialodorcontrol.com.