A heavy equipment operator is exposed to 90 dBA for 4 hours, and 95 dBA for 2 hours during their shift. According to OSHA, the permissible time ($T_c$) at 90 dBA is 8 hours, and at 95 dBA is 4 hours. Calculate their total daily Noise Dose (D).

A worker is operating a jackhammer generating 105 dBA of noise. They are wearing earplugs with an NRR of 25. Determine the actual noise level reaching the worker's ear according to the OSHA derating formula.

The OSHA Permissible Exposure Limit (PEL) for respirable crystalline silica is $50 \text{ \mu g/m}^3$ calculated as an 8-hour TWA. An industrial hygienist tests the air near a brickcutter. The pump runs at 2 liters/minute for 4 hours (240 minutes). The lab finds $0.08 \text{ mg}$ of silica on the filter. Calculate the concentration and compare it to the PEL.

A worker spends 15 years dry-cutting concrete blocks and sweeping up the dust without wearing a respirator, claiming the dust "doesn't bother them." At age 45, they develop a severe cough and shortness of breath and are diagnosed with advanced Silicosis.

A pile-driving crew works next to an active rig generating 115 dBA impact noise. They wear earplugs inconsistently because they need to hear shouted instructions from the foreman. After 5 years, a worker realizes they constantly hear a high-pitched ringing (tinnitus) and cannot understand conversations in crowded rooms.