Criterion Used Concentration/Time Test Strip Color Change time Literature adapted Rodent cut-offs (ppm) Rodent Literature Reference PEL 50 ppm/8 h ˜6 sec <100 ≤ 7 d [7] REL 25 ppm/10 h ˜ 8 sec 100/6 h [8] WVU Standard >20 ppm >7 sec ˜ 25 for 4 m [9]

Table 1: Common cut-offs based on human OSHA standards and conservative threshold values derived from the rodent literature are shown. The OSHA standards for ammonia exposure are highlighted in dark grey [10]. WVU’s adopted standard is highlighted in light grey. Since the test strips only provide a point estimate, more conservative values were selected for our use. Other convenient test strip metrics include: 10-15 sec corresponds to 10-20 ppm; <10 sec corresponds to ≥ 20 ppm; <5 sec corresponds to ≥ 40 ppm (+). REL=recommended exposure limit; PEL=permissible exposure limit.